Proposal v0.7

**tl;dr** Includes several great features/fixes by the community, as well as some sensible changes to the .gitignore list (w/ fixes for problems it causes).

* Now supports per page templates
* Now supports custom meta data in addition to that available in Pico v0.6.2
* No `Pico::get_files($directory, $ext = '')` longer loads dotfiles
* Composer now used to keep the markdown parser up-to-date
* Updated Twig version