Breaking: Drops support for Node 0.12, we now require at least Node 4.
Breaking: Update PostCSS to 6.0.0.
2.1.0
Now supports discarding duplicates irrespective of property order, better
support for legacy hacks & partial duplicate removal (thanks to @andyjansson).
2.0.2
Major performance boost by lessening algorithmic complexity; each node is
now cached and the nested loop removed, meaning that each node is cast to a
string only once (thanks to @asztal).
2.0.1
Now compiled with babel 6.
Minor performance boost from exiting from the dedupe function if the node
has less than two child nodes.
2.0.0
Upgraded to PostCSS 5.
1.2.1
Fixes an integration test failure with cssnano; use PostCSS each rather
than native forEach (thanks to @TrySound).
1.2.0
Improved duplicate detection (thanks to @TrySound).
1.1.6
Improved performance by caching string representations of nodes, and
minimising stringifying as much as possible (thanks to @TrySound).
1.1.5
Fixed an issue where comments were being deduplicated.
1.1.4
Improved performance by making all AST iterations in a single pass.
1.1.3
Improved documentation for compatibility with the plugin guidelines.
Simplify main source code.
1.1.2
Fixed an issue where declarations inside similar keyframes were being
discarded incorrectly.
1.1.1
Fixed a bug where keyframe rules were being incorrectly discarded, if they had
the same declarations but different vendor prefixes.
