Gradient Descent improvements
Merge remote-tracking branch 'upstream/master' into gradientdescent_improvements

Conflicts:
	menpo/model/pca.py
Merge pull request #368 from jalabort/gradientdescent_improvements

GradientDescent improvements
Merge remote-tracking branch 'upstream/master' into doc_toc

Conflicts:
	docs/xref_map.py
	menpo/fitmultilevel/clm/base.py