GLE - Graphics Layout Engine

With previous versions of GLE, it was impossible to use the double quote
(") character in a string because it could not be escaped. Now this works
by using (\") but now you can no longer get (\") literally. Therefore, the
TeX command \" in GLE was replaced by \'', but this does not seem to work
with the \tex{} macro. Probably the best solution is to make \tex{}
translate \'' into \".

Nice to have: support strings with ''-style quotes ala Python.