added append, prepend, and insert-child transformers
Merge github.com:Raynes/laser

Conflicts:
	src/me/raynes/laser.clj
made style changes for upstream merge
killed some accidentally remerged text
fixed variable names
converted docstring to actual English
Merge pull request #24 from silasdavis/master

Adding append, prepend, and insert-child transformers to insert children into nodes