Add support for syncing untracked files

Allows you to specify untracked files which should be uploaded when
paired tracked files have been changed. File pairs are specified in
a new .git-ftp-include file using a syntax specified in the readme.

This is useful for uploading compiled files you wouldn't want to keep
under version control, like CoffeeScript -> JavaScript or SCSS -> CSS.
Merge pull request #215 from jonathanpatt/include-untracked-files

Add support for syncing untracked files