Added Benchmark.js v1.0.0
Added benchmarkjs's nano.jar
Added Benchmark.js license to library LICENSE.md
Tree: Massive speedup in Tree#emptyNode().

Previously, `emptyNode()` triggered a node map reindex for each node
that was removed. This commit modifies `emptyNode()` to remove nodes in
last-first order and avoids the need to reindex.

Previously, emptying a node with 10,000 children took about 17 seconds
in Chrome. After this change, it's nearly instantaneous.
Build tree.
Merge branch 'master' into benchmarkjs
Merge branch 'master' of github.com:yui/yui3