Import of gtkmathview to pkgsrc-wip.

GtkMathView is a C++ rendering engine for MathML documents. It provides
an interactive view that can be used for browsing and editing MathML
markup.
GtkMathView reads MathML documents by means of a frontend whose purpose
is to traverse the MathML document (or part of it) and to appropriately
instantiate GtkMathView's internal data structures that are suitable for
rendering it.
GtkMathView renders MathML documents through a backend whose purpose is
to provide an abstraction of the platform-specific capabilities
(available fonts, drawing drawing primitives, and so on).
+gtkmathview