Fix build on Windows

Fixes #4 

### Renamed src/farmhash.cc -> src/bindings.cc

Two or more files with the name of farmhash.cc will produce outputs to the
same location. This can lead to an incorrect build result.
Fixes linker issues on Windows, as described in issue #4

### 	Added check for __GNUC__ in upstream/farmhash.cc

Checking if `!defined(__GNUC__)` prevents msbuild from erroring due to
`__builtin_expect` not existing. Original fix from Colin Riddell, see
https://groups.google.com/forum/#!msg/farmhash-discuss/xTkB3uv62pw/wAusRsWMeaAJ