Generate a constants.go

Prevent name mangling
Abort on invalid go map key types.
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