Experiment with mime magic, fail.

Incorrectly reports json and javascript files as text/plain, using file
extension instead.
Update edit command implmentation.

Assert on invalid edit command arguments (no document).

Also disable verbose middleware as it conflicts with the custom log
level configured for the program.
Implement edit for local files.

Respect --output option and handle --force when write() is passed a read
stream.
0.1.13