Consider migrating from ReadTheDocs to GitHub pages

[vitaut]

Comparison of ReadTheDocs and GitHub pages:

1. Time to load similar pages
   • GitHub: 0.70 - 1.57s
   • ReadTheDocs: 2.46 - 2.75s
2. Compatiblity
   • ReadTheDocs interferes with Sphinx builds breaking some of the features (possibly due to their customizations).
   • GitHub Pages don't interfere with Sphinx build process
3. Reliability
   • ReadTheDocs builds can remain broken for days without a way to cancel them.
   • Didn't notice any issues with GitHub pages so far.
4. Versioning
   • ReadTheDocs automates this, but versioning doesn't integrate well with the page theme except for RTD theme. However the latter has major usability issues.
   • With GitHub pages this will have to be done manually, but can be better integrated into the theme

[vitaut]

New version of the documentation on GitHub Pages: http://cppformat.github.io/dev/

Need to migrate old docs and setup redirection.

[vitaut]

Also there are some artifacts when building on Travis:

Increases the buffer capacity to hold at least *size* elements updating ``ptr_`` and ``capacity_``.

fmtlib/fmt.dev@c4caeb7

[vitaut]

Migrated the docs from RTD to GitHub pages.

• Latest release: http://cppformat.github.io/latest/
• Development version: http://cppformat.github.io/dev/