Adding History-related grunt tasks

[triptych]

This is a set of history related tasks that Dav asked to be added to grunt-yui-contrib.

history-rollup, Creates History Rollup file (Run before history-replace)
history-populate, Populates History files with @Version@ if not there already
(actually adds the whole entry e.g.

@VERSION@
------

* No changes.

)

history-replace, Replaces @Version@ in History files with release-version

[ericf]

@triptych Do you want to use this locally on the release next week, and if everything seems good and it works correctly for the full release, then we can merge and publish to npm?

[triptych]

Yeah, sounds good.