Note that you can set other options

I didn't realize this was possible until I looked at the code. It was a welcome surprise!
Merge pull request #51 from domenic/patch-1

Note that you can set other options
Added aliasDirectory option and corresponding tests.
Renamed aliasDirectory to aliasMappings to more accurately describe the feature, and updated the README.
Merge pull request #52 from bclinkinbeard/aliasDirectory

Added aliasDirectory option and corresponding tests.
directory as external option test
merged upstream/master