Added doc about possible git technologies
backlog: better CLI
Added link to pygit2 lib
Drone CI config file
Disable pyexiv2 as a pip requirement.

The package pyexiv2 is not available through PyPI.
As pyexiv2 is incompatible with python3 and deprecated it should
be replaced with GExiv2 (GObject wrapper for libexiv2).
Fixing drone config file
Switched from pyexiv2 to gexiv2
Testing with python3.3 on drone.
Merge branch 'python3' of github.com:mattgruter/picture_clerk into python3

Conflicts:
	README.md