Remove Normalize.css from `src/`, it's a dependency not Pure source code

This also removes `forms-core.css` which was effectively Normalize.css'
form related styles prefixed with `.pure-form`.
Update npm dependencies
Lock down the version of Normalize.css to 1.1.2
Simplify Grunt tasks and include Normalize.css import by default

Running `grunt` will now use Bower to install Normalize.css. As of 1.0.0
Bower got much faster, and it also uses a cache so the install only
happens once.

Added `grunt build` which does not the "import" or "test" tasks.
Tweak formatting and remove unused stuff in Gruntfile
Use bower.json to get current Normalize.css version number
Specify font stacks for grids and grid units

By setting _specific_ font stacks grids, it can be assured that the
letter and word spacing will be applied correctly. The font stack for
grid units is then set back to `sans-serif`, which is also the default
font stack that Normalize.css applied to the `body`.

Closes #41
Remove -webkit-font-smoothing: antialised
Added unminifed roll-up of everything. 'pure.css'.
Fix image resizing to be proportional

Images inside .pure-g-r when resized didn't change their height. Fix this by adding setting their height to 'auto'.
Merge pull request #170 from dchest/patch-1

Remove -webkit-font-smoothing: antialiased
Add HISTORY entry for removal of `-webkit-font-smoothing` from Buttons
add responsive images to grids manual test
add HISTORY.md entry for #172
Merge pull request #172 from dchest/patch-2

Fix image resizing to be proportional
Merge branch 'grids-tests-image'
Update font-stack with recent findings

Based on conversations in https://github.com/yui/pure/issues/41/,
this font stack was updated with more fonts to fully cover all
target environments where grids were breaking.
update HISTORY.md with #41 fix
Merge pull request #2 from tilomitra/grids-fonts

Update font-stack with recent findings
Bump version to 0.3.0-pre