Add a period archives feature and brief docs.

Allows users to have per-year, per-month, and per-day archives of posts
automatically generated. The feature is disabled by default; to enable
it a user must supply format strings for a period's respective
`_SAVE_AS` setting.
Multiple Social icons

aboutme, bitbucket, google-groups, hackernews, reddit,
slideshare, speakerdeck, vimeo, youtube

Also, fix spacing below a line-block.

Try this in resT::

	| First line
	| Second line
	| Third line

	New paragraph.

	Another paragraph.

Notice how the line-block runs into the first paragraph without the new CSS.
Creating a more explicit error message at server creation
documentation for IGNORE_FILES
Adding a message for gracefully shutting down dev server
Added missing JINJA_FILTERS documentation
Added missing SITESUBTITLE documentation
Fix typos
Merge pull request #779 from johnmastro/add-period-archives

Add period archives
Merge pull request #785 from wraithan/docs_for_ignore_files

documentation for IGNORE_FILES
Fix typos
Merge pull request #786 from noirbizarre/more-documentation

Add missing documentation for JINJA_FILTERS and SITESUBTITLE
Raise exceptions from the autoreload loop if debug is enabled
Add help directly to publishconf.py
Simple theme article permalink missing SITEURL

This change modifies the simple template so that the SITEURL
prefix is added to the article permalink found within the article
page itself.
Merge pull request #791 from wraithan/add_some_help

Add help directly to publishconf.py
Replace os.sep.join with the more robust os.path.join

From the Python docs for os.sep [1]:

  Note that knowing this is not sufficient to be able to parse or
  concatenate pathnames - use os.path.split() and os.path.join()...

Where I touched a line, I also changed double quoted string literals
to single quotes, since they are used more often in the source:

  wking@mjolnir ~/src/pelican $ git grep "'" pelican/*.py | wc -l
  683
  wking@mjolnir ~/src/pelican $ git grep '"' pelican/*.py | wc -l
  181

[1]: http://docs.python.org/3/library/os.html#os.sep
settings: Use splitext to remove extensions, not rpartition
Convert '.' and '..' to the less magical os.curdir and os.pardir

While I'm cleaning up path manipulation, I might as well make things
more semantic.
utils: Add path_to_url() and generalize get_relative_path()

The old get_relative_path() implementation assumed os.sep == '/',
which doesn't hold on MS Windows.  The new implementation uses
split_all() for a more general component count.

I added path_to_url(), because the:

  '/'.join(split_all(path))

idiom was showing up in a number of cases, and it's easier to
understand what's going on when that reads:

  path_to_url(path)

This will fix a number of places where I think paths and URLs were
conflated, and should improve MS Windows support.