Use pages instead of collections

Because of #62, #67, jekyll/jekyll#2555 and to not require building with Jekyll locally before pushing, we're [switching back to `gh-pages`](https://github.com/alfredxing/brick/issues/72).

We're doing this by switching from the use of Jekyll collections (which GitHub Pages doesn't yet support) to regular pages (and taking advantage of the `site.pages` array). This won't affect much in terms of the code and structuring, except for the `_fonts` and `fonts` directories being merged (yay!).
Otherwise, the only major change is (because Jekyll reserves the usage of `name` in page metadata), we're labelling the font names as `family` in the YAML font data files.