merging in Gilad's changes for reflection and emulation

Update article to reflect changes to APIs: use of symbols, Invocation instead of InvocationMirror.

Corrected syntax; modified from proposal to description of existing feature.

Fix a few typos

Removed references to instanceMembers etc. as API is not ready yet.

Corrections due to mirror API changes; Async stuff long gone, also latest changes

WIP. Unclear if the instanceMember API will work.

BUG=
R=gbracha@google.com

Review URL: https://chromiumcodereview.appspot.com/66333011