Config.load should grok the file type passed to it and parse appropriately

[jmanero-r7]

Per @fmitchell-r7's comment in #9 (https://github.com/rapid7/builderator/pull/9#discussion_r46425230):

I'm not a fan of encoding type information in method names, since it leads to an explosion of methods as more supported types are added. I want to be able to write code like

Config.load 'config.rb'
Config.load 'config.json'
Config.load 'config.ini'

and have the Config::File class make a best guess as to what type of file it's loading. If it makes the wrong guess, I should be able to explicitly specify type.

Config.load 'config.properties', :type => :java