upstream changed license to ALv2

Besides the license change, there are two bug fixes:
* Do not apply any transformation to the contents marked as WikiMath.
* Join sibling nodes marked as WikiMath.

Patch by: Bernhard Haumacher

(cherry picked from commit 414a61fa)

Change-Id: I6b996631ebdd908c6d96d2c9dde1a3d6dd3e212f