PackageRequirement.__str__
According to https://github.com/coala/coala/pull/4002#discussion_r108713097 , a PackageRequirement.__str__
method would be very helpful, which just returns the package name and the optional version number:
>>> str(PipRequirement('autopep8', '1.2'))
'autopep8 1.2'
>>> str(DistributionRequirement(apt_get='cppcheck'))
'cppcheck'