new README file for antlib

git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@274492 13f79535-47bb-0310-9956-ffa450edef68

proposal/sandbox/antlib/README

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+There are the following features in the antlib proposal:
+ 
+    1) antlib & antjar
+    2) type definitions that allow to define new implementations of mappers, selectors, paths, conditions, etc. That you can define in your antlib and a way to link this with the introspectors (I am not sure how complete this is).
+    3) A scoping framework for the symbol tables needed to manage the antlib definitions (I think ANT has something on this regard)
+    4) A framework for managing classloaders where you can specify which classloader to use when loading an antlib.
+ 
+(2) would be really nice, because it will eliminate all the need for mentioning classnames all around, antlibs will be used just like core.
+Also useful for tasks like <ejbjar> which has vendor specific components that should be part of the antlib of the vendor.
+ 
+(3) Probably should die and be replaced by whatever scoping thing comes from <import> proposal.
+ 
+(4) This was probably what killed <antlib> the last time around. Probably needs to be treated separately. In any case, if you load
+multiple antlibs with dependencies, there has t be a way to make them share the same classloader otherwise you cannot use it.
+ 
+So there we go, take a look at the code and let us know what you think,
+ 
+Jose Alberto & Antoine