Use OS-aware path manipulation.

Change path to filepath.  `path` is not specific to filesystem paths,
while `filepath` is. Also "./data" can be changed to "data" to make it
portable.
Calm the `golint` Gods. `Url` -> `URL` and format comments.
Use Go syntax highlight.
Merge pull request #3 from aybabtme/filepath

Fix `golint` complaints, use `filepath` instead of `path`, add color to README.