Enable to custom triangle shape

Use $width and $height to custom triangle shape, if omit $height, this
mixin will generate code in the old way. The only downside is that
$width value should always be even number, otherwise triangle width
will be short 1px.
Enable to custom triangle shape for up-left, up-right, down-left, down-right
adding package.json
adding .npmignore
Update size mixin to not accept unitless numbers

Let's just try to be explicit about this. CSS doesn't allow unitless
widths and heights, why should we? Also, there's no obvious default
one we could fall back to.
Adds font-feature-settings mixin
Accept 2-element list for `$size` and `$color`

The first value in $size would be the width value, and the second would
be the height value. The first value in `$color` would be foreground
color, and the second woud be the background color.
Add all prefixes to keyframe spec version, fixes #301

Latest versions of chrome are using the keyframe spec version but are ignoring unprefixed animations. Adding prefixed versions to spec keyframes fixes this.
More flexibility in button mixin

Issue #160
Added "inset-up, inset-down, inset-left, inset-right" four arguments to $direction

Please see http://codepen.io/P233/pen/AtzIw for more details.
Fixing missing check for color values in _background-add-prefix
fixed typo in _modular-scale partial
Merge pull request #334 from vis-kid/master

fixed typo in _modular-scale partial
Update position add on to utilize false/null rather than unitless zero values.
Update readme.md

Just cleaning it up a bit. All the underlines and such look ugly. :)
Add css3 filter support

Currently, MDN says only the -webkit prefix is supported, so that's all
that's included.
Fix typo in columns mixin (thoughtbot/bourbon#342)
Merge pull request #346 from shreve/master

Add css3 filter support
Merge pull request #340 from corysimmons/patch-1

Update readme.md
Merge pull request #327 from kvakes/master

Fixing missing check for color values in _background-add-prefix