Begins jinja2 support as mentioned in ARMmbed/yotta#90
add jinja2 to dependencies, remove Cheetah
Add Python3 to .travis.yml
Revert "Add Python3 to .travis.yml"

This reverts commit 74bf7eafdffa76be18283e4d08e210ebdaba41da.
cmake syntax fixes; fix variable name
Merge pull request #92 from matthewelse/jinja2

Continue with Python3 support (using jinja2)