Adds numeric iOS versioning option.

Setting versioning_method on deployment_target to 'commits' will use
the number of commits in the current branch to set the build number.
Anything else (or blank) will use the current git SHA.
Adds Joe Masilotti to authors.
Merge pull request #27 from joemasilotti/master

Adds incremental iOS versioning option.
user can specify upload token as an environment variable [#66358934]
include example.yml in the README