All HTML code and Doxygen shortcuts such as @c, @b and @em are now
rewritten using Markdown syntax, which makes it more readable.
Also updated Doxyfile. Doxygen 1.8 at least is required to generate
the documentation now.
AbstractImporter now provides access to the data directly and doesn't
attempt to do any OpenGL stuff, thus making everything more transparent
and testable.
Start of AbstractImporter rework - Trade namespace will contain simple
classes usable for exchanging data with other formats, importers will
not depend on any OpenGL functionality, they will just provide access to
plain data.
Each importer must now specify whether it can open files or streams in
features() and implement one or both open() functions. Default
implementation of open() functions now prints message on error output
and returns false.