Turning `git describe` into acceptable PyPi version strings.

git2pypi.sh

# Assumes releases are tagged with "vMAJOR.MINOR.PATCH" (semver)
# The first sed removes the leading "v" (this step is not entirely necessary)
# The second sed uses the "number of commits since tag" to create a dev version and uses the sha as the "local version"
#
# If the second sed fails, it will just print the returns of the first sed
#
# Sample output: 
#   0.3.0.dev1+g7a45b05
#   0.3.0.dev3+g8418ac6.dirty
#   2.7.1rc2.dev17.dirty
git describe --tags --always --dirty=.dirty | 
sed 's/v\(.*\)/\1/' | 
sed 's/\([0-9][0-9]*\.[0-9][0-9]*\.[0-9][0-9]*\)\(rc[0-9]*\)\{0,1\}-\([0-9][0-9]*\)-\(g.*\)/\1\2.dev\3+\4/'