Support ordering pages and articles when iterating in templates.
Order can be set to a metadata attribute or a sorting function.
Default to order by slug for articles and order by filename for pages.
Add test for PAGE_ORDER_BY
Test to reproduce an issue that occurs with python3.3 under macos10 only

This test passes fine under linux
enable writing of only selected output paths

- add WRITE_SELECTED setting
- add --write-selected commandline option
set _cache_open func even if not loading cache, fixes autoreload

The _cache_open attribute of the FileDataCacher class was not set when
settings[load_policy_key] was not True, so saving later failed.
As a precaution, replaced the `if ...: return` style with a plain
if structure to prevent such readability issues and added tests.
Merge pull request #1314 from smartass101/write-selected-only-PR

Enable writing of selected output paths only. Refs #224.
Merge pull request #1318 from smartass101/fix_cacher_open_func

set _cache_open func even if not loading cache, fixes autoreload
Handle list metadata as list of string in MarkdownReader
Ability to specify PLUGIN_PATH as list
PLUGIN_PATH added to settings table
Text tweaks for "PLUGIN_PATH as list" feature
Make docutils requirement explicit. Fixes #1243.

Previously, the error returned by Python when docutils is not installed
was not explicit, instead saying that HTMLTranslator is not defined
(needed by FeedGenerator and such), forcing the user to go into
readers.py to figure out that this happens because "import docutils"
failed.

This pull request makes the docutils dependency explicit, so that there
is an ImportError if doctutils is not found.
Add feeds for each author
Merge pull request #1310 from eincs/handle-multiline-meta-in-markdown

Handle multi-line meta in markdown content properly
split content caching into two layers

This is a reworked and improved version of content caching.
Notable changes:
- by default only raw content and metadata returned by readers are
  cached which should prevent conficts with plugins, the speed benefit
  of content objects caching is not very big with a simple setup
- renamed --full-rebuild to --ignore-cache
- added more elaborate logging to caching code
Merge pull request #1320 from smartass101/cache_raw_content

split content caching into two layers
Merge pull request #1313 from al-tonio/frenchdate

Test to reproduce problem with Python 3.3+ on Mac OS X only
send the static_generator_{init, finalized} signals.

Note: The two signals were already present but were never sent.
use correct CachingGenerator class in super() call

This was a leftover from code moving in c1324b0.
Detected by pylint.
Merge pull request #1329 from smartass101/fix_caching_subclass_super

use correct CachingGenerator class in super() call
Merge pull request #1328 from Scheirle/StaticGeneratorSignals

Send the static_generator_{init, finalized} signals