Add a requirements file for Sphinx
Run sphinx-quickstart
Tune Sphinx

Mainly remove unused options, and extract the version from flycheck.el
Replace Texinfo targets with Sphinx targets
Ignore Sphinx build output
Use code as default role
Add a little front matter and the license text
Add target for the link check builder
Fix the info target
Bump minimum Sphinx version for good texinfo support
Build an info file to doc/

We will commit this for MELPA
Port the Introduction section
Configure Texinfo build
Remove duplicate target
Ignore generated Python bytecode
Remove superfluous extension
Add domain for Emacs Lisp symbols
Improve the appearance of the annotation
Add support for macros
Port the selection section from the usage chapter