Merge pull request #225 from alxhub/proto

Initial, experimental proto support in Streamy.
reorg code a little in bin/mixologist.dart
tiny abstract file system API
move mixing logic from transformer into common function
remove debugging
refactor bin/mixologist.dart to use common code
rename mixologist binary to "mix"
add comments
Merge pull request #227 from yjbanov/sync-v0.2

Consolidate mixologist generator code
Working on tests for proto generation.
consistent quotes
cleanup equality utilities
add tracing events to ProxyClient and JSON parser
optional marshallers and API resources; generate RawEntity; port tests
is_map mixin
fixes in http handler code
make error handling in SimpleRequestHandler behave like ProxyClient does
close streams on errors; nested microtasks do not affect onDone
freeze entity in ProxyClient
honor request headers even without a payload, and add withCredentials support