allow override page url and save_as values directly from the metadata

this is similar to the template override implemented in #404
add functional test for save_as/url override

and update functional tests output
add docs for save_as/url override from metadata feature
Merge pull request #623 from bbinet/url-save_as-override

Override page 'url' and 'save_as' directly from the page metadata. Fixes #400.
Fix the tag cloud example
add disqus_url to comment js block
update the output files
Fixes #645 - Making cross-content linking windows compatible
Move the tests into pelican. Fix #500
generators: Teach Generator.get_files to handle non-directory input

This makes it easier for StaticGenerator to walk FILES_TO_COPY, where
the input may be a directory or a bare filename.

Non-traversable file types (e.g. everything but directories and
symlinks to directories) are not checked against the exclude list.
The user-level effect of this is that explicit entries in STATIC_PATHS
or FILES_TO_COPY will override a hypothetical STATIC_EXCLUDES setting,
which seems like a reasonable approach.

I also removed the Python 2.5 compatibility check for `followlinks` in
os.walk, since Pelican is now Python >=2.7.
endswith can take a list as an argument ;)
Fixed the stopserver command to use the correct Makefile syntax
Fixes the reST syntax of an example in the docs

reST example of the section "Linking to internal content" had incorrect
metadata. Moreover, time was missing from the date of both markdown and
reST example.

This was pointed out by [lefromage at #pelican](https://botbot.me/freenode/pelican/msg/2235275/)
Merge pull request #764 from talha131/master

Fixes the reST syntax of an example in the docs
Merge pull request #762 from tthurman/master

Fix stopserver command
Merge remote-tracking branch 'upstream/master'
fix disqus urls in test pages