AddGoComments can not use "windows" paths with backslash

This is not a big issue but I noticed that on windows when constructing paths using path.join or related the comments
did not load. But if I replaced all the backslashes (normal microsoft) with slashes (the rest of the world) it works.

Slashes works
`reflector.AddGoComments("github.com/lavoqualis/messages.go", "./sources" )`
but backslash
`reflector.AddGoComments("github.com/lavoqualis/messages.go", ".\\sources" )`
doesn't.

Start at the reflector.AddGoComments entry point and reproduce the two documented calls on Windows, comparing forward- and backslash paths. Trace how the source path is resolved and verify that the backslash form loads comments successfully without breaking the existing slash form.

Written by the indexing model from the issue text.