Fix generator for multiple services.

Only generate the RPCClient interface stub once per package. This allows multiple services.
generator: truncate destination file
Fix exception response handling in generator code
Add parser support for single quoted strings
Merge pull request #31 from dougm/parser-quoted-string

Add parser support for single quoted strings
Add test for oneway client requests
Merge branch 'master' of github.com:samuel/go-thrift