Add algorithm for computing immediate dominators
Add immediate_dominators to documentation
Add algorithm for computing dominance frontiers
Add dominance_frontiers to documentation
Fix reference syntax in dominance.py
Merge pull request #1241 from ysitu/dominance

Add algorithm for computing immediate dominators and dominance frontiers
Add pypy3 to Travis test matrix
Fix download link to IronPython binary
Change path to MathJax CDN

See http://www.mathjax.org/changes-to-the-mathjax-cdn/ for details