Added MicrosoftLogging project + LogAdaptor

The Log event needed to be added to IDiscordClient to allow
MicrosoftLogging to compile implementation-agnostic. This has no major
effect on any of our libraries, and should have minimal effect on any
downstream libraries.

Discord.Net.sln

@@ -1,6 +1,6 @@
 Microsoft Visual Studio Solution File, Format Version 12.00
 # Visual Studio 15
-VisualStudioVersion = 15.0.26730.12
+VisualStudioVersion = 15.0.26730.3
 MinimumVisualStudioVersion = 10.0.40219.1
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Discord.Net.Core", "src\Discord.Net.Core\Discord.Net.Core.csproj", "{91E9E7BD-75C9-4E98-84AA-2C271922E5C2}"
 EndProject
@@ -24,6 +24,8 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Discord.Net.Tests", "test\D
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Discord.Net.Webhook", "src\Discord.Net.Webhook\Discord.Net.Webhook.csproj", "{9AFAB80E-D2D3-4EDB-B58C-BACA78D1EA30}"
 EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Discord.Net.MicrosoftLogging", "src\Discord.Net.MicrosoftLogging\Discord.Net.MicrosoftLogging.csproj", "{3FDEFF51-286A-4D2F-AD73-3679A76F09B5}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -130,6 +132,18 @@ Global
 		{9AFAB80E-D2D3-4EDB-B58C-BACA78D1EA30}.Release|x64.Build.0 = Release|Any CPU
 		{9AFAB80E-D2D3-4EDB-B58C-BACA78D1EA30}.Release|x86.ActiveCfg = Release|Any CPU
 		{9AFAB80E-D2D3-4EDB-B58C-BACA78D1EA30}.Release|x86.Build.0 = Release|Any CPU
+		{3FDEFF51-286A-4D2F-AD73-3679A76F09B5}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{3FDEFF51-286A-4D2F-AD73-3679A76F09B5}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{3FDEFF51-286A-4D2F-AD73-3679A76F09B5}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{3FDEFF51-286A-4D2F-AD73-3679A76F09B5}.Debug|x64.Build.0 = Debug|Any CPU
+		{3FDEFF51-286A-4D2F-AD73-3679A76F09B5}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{3FDEFF51-286A-4D2F-AD73-3679A76F09B5}.Debug|x86.Build.0 = Debug|Any CPU
+		{3FDEFF51-286A-4D2F-AD73-3679A76F09B5}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{3FDEFF51-286A-4D2F-AD73-3679A76F09B5}.Release|Any CPU.Build.0 = Release|Any CPU
+		{3FDEFF51-286A-4D2F-AD73-3679A76F09B5}.Release|x64.ActiveCfg = Release|Any CPU
+		{3FDEFF51-286A-4D2F-AD73-3679A76F09B5}.Release|x64.Build.0 = Release|Any CPU
+		{3FDEFF51-286A-4D2F-AD73-3679A76F09B5}.Release|x86.ActiveCfg = Release|Any CPU
+		{3FDEFF51-286A-4D2F-AD73-3679A76F09B5}.Release|x86.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -141,6 +155,7 @@ Global
 		{688FD1D8-7F01-4539-B2E9-F473C5D699C7} = {288C363D-A636-4EAE-9AC1-4698B641B26E}
 		{6BDEEC08-417B-459F-9CA3-FF8BAB18CAC7} = {B0657AAE-DCC5-4FBF-8E5D-1FB578CF3012}
 		{9AFAB80E-D2D3-4EDB-B58C-BACA78D1EA30} = {CC3D4B1C-9DE0-448B-8AE7-F3F1F3EC5C3A}
+		{3FDEFF51-286A-4D2F-AD73-3679A76F09B5} = {CC3D4B1C-9DE0-448B-8AE7-F3F1F3EC5C3A}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {D2404771-EEC8-45F2-9D71-F3373F6C1495}

src/Discord.Net.Core/IDiscordClient.cs

@@ -7,6 +7,8 @@ namespace Discord
 {
     public interface IDiscordClient : IDisposable
     {
+        event Func<LogMessage, Task> Log;
+
         ConnectionState ConnectionState { get; }
         ISelfUser CurrentUser { get; }
         TokenType TokenType { get; }

src/Discord.Net.MicrosoftLogging/Discord.Net.MicrosoftLogging.csproj

@@ -0,0 +1,15 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <Import Project="../../Discord.Net.targets" />
+  <PropertyGroup>
+    <AssemblyName>Discord.Net.MicrosoftLogging</AssemblyName>
+    <RootNamespace>Discord.MicrosoftLogging</RootNamespace>
+    <Description>A Discord.Net extension adding support for Microsoft's logging abstractions.</Description>
+    <TargetFrameworks>netstandard1.1</TargetFrameworks>
+  </PropertyGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\Discord.Net.Core\Discord.Net.Core.csproj" />
+  </ItemGroup>
+  <ItemGroup>
+    <PackageReference Include="Microsoft.Extensions.Logging.Abstractions" Version="1.1.1" />
+  </ItemGroup>
+</Project>

src/Discord.Net.MicrosoftLogging/Extensions.cs

@@ -0,0 +1,14 @@
+using System;
+using Microsoft.Extensions.Logging;
+
+namespace Discord.MicrosoftLogging
+{
+    public static class Extensions
+    {
+        public static void UseMicrosoftLogging(this IDiscordClient client, ILogger logger, Func<LogMessage, Exception, string> formatter = null)
+        {
+            var adaptor = new LogAdaptor(logger, formatter);
+            client.Log += adaptor.Log;
+        }
+    }
+}

src/Discord.Net.MicrosoftLogging/LogAdaptor.cs

@@ -0,0 +1,29 @@
+using System;
+using System.Threading.Tasks;
+using Microsoft.Extensions.Logging;
+
+namespace Discord.MicrosoftLogging
+{
+    public class LogAdaptor
+    {
+        private readonly ILogger _logger;
+        private readonly Func<LogMessage, Exception, string> _formatter;
+
+        public LogAdaptor(ILogger logger, Func<LogMessage, Exception, string> formatter = null)
+        {
+            _logger = logger;
+            _formatter = formatter ?? DefaultFormatter;
+        }
+
+        public Task Log(LogMessage message)
+        {
+            _logger.Log(GetLogLevel(message.Severity), default(EventId), message, message.Exception, _formatter);
+            return Task.Delay(0);
+        }
+
+        private string DefaultFormatter(LogMessage message, Exception _)
+            => message.ToString();
+        private static LogLevel GetLogLevel(LogSeverity severity)
+            => (LogLevel)(Math.Abs((int)severity - 5));
+    }
+}