Windows paths fix

[chukonu]

This branch tries to fix the issue with file paths on Windows, as Windows uses backslashes instead of forward slashes.

A proxy library, upath, is included to replace the original reference to the built-in module path.

In loader.js, path#basename is used instead of String#replace to retrieve the last portion, excluding the file type suffix, of a path.

[coveralls]

Coverage decreased (-23.31%) to 76.69% when pulling c312cdc on tiaoshi:windows-fix into 46a78b8 on zedgu:master.

[coveralls]

Coverage decreased (-23.31%) to 76.69% when pulling c312cdc on tiaoshi:windows-fix into 46a78b8 on zedgu:master.

[zedgu]

Thank you for your work.
But it failed the test for now, I'll marge the PR when CI build passed.

[chukonu]

Thanks for your reply, Zed. I'll try again.