Load literate user settings

This provides support for literate (`.org`) files to be used for package specific customizations via `el-get-user-package-directory`.

I based it in part off of #539 and off of the method used by Eric Schulte in [Emacs 24 starter kit][1].

It provides customizable variables for supported file extensions as well as a fairly simple way of adding other loadable file-types that might currently or one day exist (a new variable and a single line in the `or` statement is needed for each additional type).

It does not check to ensure that only one file will match and be loaded.  This is impossible because `org-babel-load-file` creates a `.el` file with the same name.  Since this new file is not compiled by babel I also removed compilation of `.el` files so that they will all be loaded the same way.  Changing this would require adding a function that compiles then loads the file, and setting `plain-type-load` to that function.

The `(catch ... (throw ...))` loop ensures that only the first matching extension will be used, the custom variables used for file extensions are in the order they will be checked and give priority first to encrypted, then to compressed formats.


[1]:http://eschulte.me/emacs24-starter-kit/#sec-2-3