Restructure the repository

1. Use "gopath" as GOPATH instead of the entire directory.
2. Use single Makefile structure instead of recursive Makefile.
Swap Makefile target test and check

1. Use `make check` for unit testing
2. Use `make test` for integration test
3. Hide commands in `make check` (easier to read)
Start building test for OAuth interface

Only a dummy test function now