First pass at CachingRequestHandler.
Final refactor finished.
Add a few events to track.
Test for PRIMARY -> SECONDARY translations in MultiplexingRequestHandler.
Changes for code review, and comments.
Merge PR 131 into master
Fix typo in batching_test.dart
Fix noRpcAge and add tests
Address review comments; cache code clean-up; more cache tests
Merge pull request #177 from yjbanov/request-handler-split

Multipexer split + merge + fixes