Macrel

* Make atomicwrites an optional dependency

* Add --log-append flag
* Add --log-file argument
* Add usage example in command line help message
* Use atomic writing for output

* Fix bug with Prodigal by changing internal parameters
* Fix bug with using --force and existing directories
* Add version to header in output table

* Remove Methionine from N-terminus
* Fix for when no smORFs are present
* Add --keep-negatives flag
* Add warning for longer sequences

* Fix for Python 2.7

* Add get-examples command
* Add get-smorfs command
* Convert to scikit-learn
* Updated training sets
* Fix license (must be GPL because of Peptides)