Create ipad-above mixin.

This mixin defines the media query for all screens above 768px, which previously didn't exist.
Bugfix: Make %row extend %clear instead of .clear.

Previously, %row would not clear as expected if $classes was false.
Create helper mixins

- Users of groundwork looking for semantic implementations can now include instead of extend helpers (e.g. "@include _pad-left;"). This is particularly useful for media queries - at the moment extends within @media queries don't work the way you would expect them to, but mixins do. There are now 3 ways to utilise layout helpers - as mixins, as placeholders, and as classes.
- mixins have been given an _underscore prefix, because of uncertainty regarding name clashes and potential for confusion (e.g. "border-bottom" could be both a CSS property and a mixin - this may or may not be considered an issue). Make a decision as to whether to keep or axe the prefix. The -dash prefix is also worth considering.
- It'll be good to have a 3-column table somewhere on a page saying "hey guys, you can activate a layout helper in 3 ways. E.g. _pull-right, %pull-right, and .pull-right" and so on.
Merge branch 'master' into helper-mixins

Conflicts:
	src/scss/_helpers.scss

Seems like truncate is a new thing. Added it in.
Restructure tests folder

Tests folder is now structured for test-driven development if any dev wants to develop that way. Each test consists of a simple page + CSS generated with Jade/SCSS. Note that for space reasons, compiled CSS is not included, you have to compile tests/src/scss/(whatever).scss into tests/(whatever).css locally.

Did up a first test for grids, which expands on whatever was in the test folder before this. Looks good - seems like grid divisions, re-ordering, offsetting, and centering work as expected for extends. Mobile adjustments aren't extend-ready yet - someone should work on this in future.
Add test for helpers to the tests folder

- This was done in order to test upcoming helper-mixin functionality (currently unmerged in a separate branch).
- Looking at the test, it seems like extends are working the same as their class counterparts. Will update the test for includes once this branch is merged with helper-mixins.
- rotate-90s and rotate-270s overflow around their containers. Is this a bug or is the test usage of them wrong or what? To be looked at in future.
- Removed obsolete test.jade (Forgot to remove this in the last commit).
Merge branch 'tests' into helper-mixins
Update test for helpers with tests for includes

- Now that helpers-mixins and tests have been merged, updated tests to check that helper-mixins are working correctly. They seem to be.
- "truncate" seems missed out from the class list for generating classes. Added it.
Merge branch 'master' into helper-mixins
Merge based on the latest upstream commit

Take note:
- Disabled added in to helpers.
- Removed test.css (because we have test-helpers.scss and test-grid.scss)
- Recompiled groundwork.css.
Merge helper-mixins based on latest upstream (4 Apr 2013).

Conflicts resolved:
- tests/*.css and idea/* added to .gitignore.
- Consolidated changes in _helpers.scss.
- Do we have a need for test.css? Removing it. (the new tests rely on their own specific test-(whatever).css file.)
Merge commit 'b358d903bb1e9b9f57a1857f7ebd40d10324bcb2' into helper-mixins

Conflicts:
	tests/src/scss/test.scss
	tests/test.css

Git-removed those files.
Merge pull request #69 from Sneakertack/helper-mixins

Helper mixins + Groundwork tests