In preparation for caching we store the MathML fragment returned by
local checker. The rational is that the string serialization of the
parse tree is better chachable as the parsetree.
Change-Id: Ice2ef1f4f7b83ed187507d4d067f446603d0d6a5
In perparation to the PHP only native MathML rendering mode, we expose
the parsetree of the checker.
Change-Id: I8da8d0e236c2b001e664ce707c7469ebe8a91eb8