Add support for loading a single .tern-project file

[mortalapeman]

While configuring tern through the default behaviors is definitely a route to take, it would be nice to offer a behavior that reads a .tern-project file and sends it to the server. Any relative file paths would need to be converted to absolute path, relative to the file's location.

[bfricka]

Agreed, and it should be: :lt.plugins.tern ← $HOME/.tern-config ← .tern-project