Caching added to #articles and #sorted_articles

Added caching for #articles and #sorted_articles to speed up for may items.
only cache when preprocessing is ready

Only cache these values if preprocessing is ready. Preprocessing is ready when the
@items attribute is frozen.
removed unneccessary line for returning instance variable
Silence "Could not find files for the given pattern(s)" message on Windows
Add release notes for 3.6.3
Update version to 3.6.3
Improve notification tool detection
Merge branch 'bug-quiet-watch-on-windows' into release-3.6.x

Conflicts:
	lib/nanoc/cli/commands/watch.rb
Update release notes
Remove autocompiler
Remove watcher
Fix new failing test_filter_html_doctype test
Fix YARD parsing order errors
Fix failing link_to test
Fix teardowns with missing super
Remove requires for removed code
Remove Markaby filter
Teardown listeners after compile
Setup listeners only once
Set Ruby 1.9 as the minimum Ruby version