Simplify

PKG_CHECK_MODULES calls AC_SUBST already.
Move options next to related code
Organise configure.ac a bit
Organize configure.ac a bit
The custom reader does not seem to need libxml2
Fix enabling/disabling libxml2 reader
Simplify mathvariant code

Simply commit the generated source code (with a bit of modification) and
remove the convoluted way used to generate that, it is not like this
mapping changes often (if at all). This has the side effect of
simplifying cross-compiling.
We always get the area & factory from the context

So simplify things and pass only the context.
Move the math variant mapping to the shaper

The graphics device have no business doing such mapping, that is the
shapers job.
Fold libmathvariants into libbackend_common

It is not used anywhere else.
Comment this out for now
Do math variant mapping even in text mode for now