Bump version to 0.5.0 and add release notes

BUG=
[email protected]

Review URL: https://chromiumcodereview.appspot.com//1372113004.

rename FieldType to PbFieldType and bump version to 0.4.2

'FieldType' conflicts with classes and proto messages with the
same name. Renamed to PbFieldType to make this less likely.

(I'm breaking compatibility with 0.4.1 because leaving
'FieldType' around will prevent upgrades from 0.4.0
and below. Since I just released 0.4.1 on Friday, it
seems unlikely to affect many people.)

BUG=
[email protected]

Review URL: https://chromiumcodereview.appspot.com//1312763005.

bump version to 0.4.1

bump version to 0.4.0

buildbot: don't run reserved_names_test using dart2js

Fix GeneratedService and RpcClient to be independent of wire protocol.

Oops, broke dart2js. (Will be included in 0.3.9.)

bump version to 0.3.6