Travis CI + Pandoc for autobuild docs (*.md -> *.pdf)

[ghost]

Setup .travis.yml for converting Markdown docs to PDF automatically on each commit and upload resulted PDF back on Github (in separate branch)

• https://gist.github.com/willprice/e07efd73fb7f13f917ea
• https://github.com/jgm/pandoc/wiki/Using-pandoc-in-Travis-CI
• https://github.com/mkulesh/microMathematics/tree/master/autobuild

REFERENCE

• https://pandoc.org/demos.html
• http://vaibhavsagar.com/blog/2015/02/26/automate-resume/