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.
Empty file for windows docs.
Some beginning collection for Windows users.

Leaving the office so it's a bit unkempt.
Add additional information about encoding issues on Windows
Add note about auto-regeneration
Add block of code which should be added to Gemfile for Windows listen compatibility.

Closes https://github.com/mojombo/jekyll/pull/1720
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.
Remove trailing whitespace
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.