travis: use requirements files instead of one by one list
py25: drop remant of 2.5 support
travis: build docs with warnings as errors
docs: add _static dir just in case
flask: drop flaskext_compat

If we bump up our minimum requirements we can drop this compat layer.
psyco: drop it, it is unsupported

While it might work on Python 2.6, most people won't be running on that
anyway and we won't be for amagama.locamotion.org

So remove it so we don't need to maintain it.