Sort plugins so people can have "load orders".

This allows for people to do something like "_plugins/1-autoload-global.rb" and have it load first and so on making it much easier to organize code and have a "header file" that does all the requiring up front if it's needed for all plugins.
A start at a gem-based plugin whitelist for Pages.
Add --whitelist flag and internal logic
Remove Site.whitelist attribute.
Add syntax for mercenary CLI engine by @mojombo
Fix serve -> server alias, ensure --drafts is mapped to show_drafts
Switch from commander to mercenary in gemspec
Let jekyll-import specify subcommands and their options for each importer.

@mojombo, this look better?
Check if JekyllImport is defined using Object#const_defined?
If no args are given, then list possible importers.
Parse TOML or YAML in Jekyll::Configuration.
Better config file parser error if it's not there.
Give that LoadError a good message.
require the TOML gem, idiot.
Add some unit tests for TOML integration.
Fix favicon’s type
Update requirements to maruku 0.7
Remove extraneous newlines from XHTML output
Fix tests to expect maruku 0.7 output
Merge pull request #1772 from penibelst/no-x-icon

Fix favicon’s type