Generate a constants.go

Prevent name mangling
Correct oproto nil check
Fix go get url
Don't mangle target package directory.
Simplify go example code
Code cleanup and shortening.

Place thrift metadata into field tags.
Unexport StreamTransport field
Simplify types.go
Simplify by removing removing TStruct

Change TField to be unexported field
Simply generated service api
Remove unused TBase
Abort on invalid go map key types.
Properly render methods if field indices are negative
Render literals for structs
Emit go types
Wrap structs and bytes
Declare vars in deserializers if needed.
Simplify error handling