Become a proper NPM package

- Reorganize the file structure to be less messy
- Add a git-tree-srv wrapper script that will require CoffeeScript and
  then server.coffee
- Fill out package.json
Finish the response once git's stdout is closed

If the 'git cat-file' exits on the same tick as it has writable data in
the socket we can finish the response before the remaining data arrives.
Instead finish the response in stdout is closed which seems cleaner
anyway.
Add some more friendly messages

- Print a message once we've started up
- Reference the example config file if we're invoked without one