Make template.py more generally applicable

[tovrstra]

I've made a few improvements:

• keep .yml extension, so syntax highlighting still works on the template files.
• move variables to a separate file, so the script becomes standard as well.
• loop over all template files in tools dir, so we can do the same with other files.

I'm not entirely happy with this. Using the .travis.yml file as its own template would make things a lot easier.

[matt-chan]

Hmm yes I like this format better. Looks good!