Break Apart Typeplate

Hey Guys,

I am submitting this pull request to see what you guys think about breaking apart the Typeplate lib.

I've done a quick breakup of the file structure, but did very little to clean up comments, etc. So this pull-request will likely need some work, if you're even interested at all.

*The use case is a multi-page setup with SCSS.*

**For example:**

1. I might create a _core.scss that includes mixins, functions and other scss utilities that add no additional css. This include is shared across top-level (i.e., scss files that do not start with an underscore). 
2. Subsequently, create a a **global.scss** file that imports all of the shared SCSS that creates styles, e.g., helper classes, normalize, resets, etc. 
3. Finally, each page in the site gets it's own top level file and imports that are unique to that page.

My struggle right now is that _typeplate.scss adds SCSS that ultimately creates CSS and it becomes impossible to accommodate the above use case.

**Updates (from the commit log):**
  - moved vars into ./config because it's more of a configuration file
  - renamed vars to create a consistent naming convention
  - moved default vars into _defaults
  - moved placeholders in to _extend
  - moved font related styles into _fonts
  - moved functions into _funtcions
  - moved helper classes into _helpers
  - moved reset (typeplate normalization) styles into _resets
  - reused _typeplate as a macro to import all files that do not create
    additional css (defaults, functions, mixins, extends)
  - created _typeplate-styles to import all files that create css
    (resets, helpers, fonts)