Fix typo in readme.md

- Fixed all test cases to use using(Buffer)
- Fixed all test cases to explicitly specify session

They are managed by GC.

PowerShell script is apparently malfunctioning to extract files from the linux
archives.
More testing (and fixes) will follow.

Let's keep things clean and neat.

* Refactored DisposableObject

* Added different build directory for TensorflowNET.Examples.GPU

* _FetchHandler: Switched to NPTypeCode

* gfile.cs, Walk(...): Handle case when directory top doesn't exist.

* Tensor.Creation: Perf-opted when creating tensor from NDArray of string

* Graph.cs: refactor and added docs

* Tensor.Creation.cs: perf-ops

* Tensor.Explicit.cs: perf-ops

* Copied globals.regen from NumSharp

- Added supported_numericals_TF_DataType

* Tensor perf-ops and cleanup, Revamped dtypes.cs, some renames.

- Cleanup and docs to all Tensor.cs files
- Changed all uses of System.Convert to NumSharp.Utilities.Converts
- Added all missing types in dtypes.cs
- Renamed tensor.Data<T> to tensor.ToArray<T>, added obsolete message
- Renamed tensor.Data() to tensor.BufferToArray(), added obsolete message
- Made GraphKeys to use const string instead allocating strings at every use of GraphKeys.

* Tensor: Added guards for explicit casts.

* Tensor: Added explicit cast to string

* Tensor.ToArray<T>(): Added support for cases when tensor is scalar.

* Tensor.BufferToArray(): Fixed to use long instead of int.

* TensorShape: Revamped and documented.

* BaseSession: Added Session.run(ITensorOrOperation fetche, params FeedItem[] feed_dict)

* Tensor: renamed _dtype to _override_dtype

- Fixed all locations _dtype is used incorrectly.

* Fixed unit tests

* Tensor.Operations: Reverted commit

* DisposableObject: sorted internal_dispose to properly handle Dispose() calls

* Tensor.DisposeUnmanagedResources: Nullify _handle after delete.

* TensorShape.this[...]: fixed guard check.

* DisposableObject #362

This project can be used to generate a nuget holding tensorflow cpu
libraries for windows and linux runtimes.

The Copy-NativeTensorFlowLibs.ps1 script can be used to download all the
libraries from Google.

The examples have been updated to use this nuget to check that things
are working.
(Make sure to update your package source to have the packages directory
in your nuget source before trying this at home).

The library necessary to pack the nuget can be downloaded with the
Copy-NativeTensorFlowLibs.ps1 powershell script.