xml => lxml for bs4, in pelican-import.wp2fields()
Fixes issue in devserver introduced in v3.3

Fixes an intermittent devserver problem with directory urls
containing index.html (i.e. clean urls).  It tries to send the
index.html file twice, resulting in a scrambled web page complete
with HTTP headers in the output, and sometimes Broken Pipe errors.
Add period to period_archives context. Refs #1044.

* Adds period tuple of (year, month, day) matching the time
  period of the current archive. Note that this is done
  to the archive context if period_archives.html doesn't exist.
* Adds tests to verify this.
* Adds documentation in themes.rst about period in period_archives.html.
add signal article_generator_pretaxonomy

invoked before categories and tags lists are created
useful when e.g. modifying the list of articles to be generated
so that removed articles are not leaked in categories or tags
Clarify docs re: settings file
Merge pull request #1249 from smartass101/split_articles_generate_context

Add article_generator_pretaxonomy signal
Merge pull request #1246 from fenekku/period-to-archive-context

Add period to period_archives context. Refs #1044.
PY and PELICAN env variable overrides for Make

This allows the user to set PY and/or PELICAN environment variable
overrides, which will be respected by the Makefile and devserver.sh.
If, for example, the default Python on your system were Python 3 and
you wanted to run Make with Python 2, using bash you could run
`PY=python2 make`. Refs #915.
Merge pull request #1178 from robulouski/devserver_fix

Fix issue in devserver introduced in v3.3
Merge pull request #1114 from brannerchinese/master

xml => lxml for bs4, in pelican-import.wp2fields()