* Install deps.
* Ensure test fails if deps are missing.
* Update dictionary for recent docs changes.

Update install docs.

Use console_scripts entry_point instead of manually built script.

The sdist command now builds the MANIFEST automatically. No need
to do it manually. Also, PyPI now only accepts one sdist file per
release, so let's not try to upload two.

Also, the docs deploy command does not work right so it's removed.

This version was released to force PyPI to point to the new docs location.
Closes #601. The old PyPI hosted docs can be deleted after this.

Fixes #601. Merged in 6f87b32 from the md3 branch and did a lot of cleanup.

Changes include:

* Removed old docs build tool, templates, etc.

* Added MkDocs config file, etc.

* filename.txt => filename.md

* pythonhost.org/Markdown => Python-Markdown.github.io

* Markdown lint and other cleanup.

* Automate pages deployment in makefile with `mkdocs gh-deploy`

    Assumes a git remote is set up named "pages". Do

        git remote add pages https://github.com/Python-Markdown/Python-Markdown.github.io.git

    ... before running `make deploy` the first time.

Ancestry exclusion for inline patterns.

Adds the ability for an inline pattern to define a list of ancestor tag names that should be avoided. If a pattern would create a descendant of one of the listed tag names, the pattern will not match. Fixes #596.