DirichletDiscrete: get the signs consistent

this shuts up sign compare compile errors
Merge pull request #68 from stephentu/baseline

DirichletDiscrete: get the signs consistent
Reenable -Wsign-compare as suggested by Stephen
Make distributions.io.stream helpers consistently makedirs
Add version badge to readme
Make protobuf methods consistent across python,C++
Merge remote-tracking branch 'origin/master'

Conflicts:
	CMakeLists.txt