Move hashing to module, Add fileSha support

The build fingerprint varies more then just the source code (git sha)
and needs to be more unique then a normal git sha. Otherwise the same
git sha can yeild invalid links to asset files on s3. Using the SHA hash
of the index file it will be unique to each build instead of each
commit.
Add support for S3 ContentType

With out this S3 will assume all files are application/octet-stream and
server them as such. We needs to detect our own.
jshint clean up and TODO comment
Bump version to 1.2.0