Remove the 'hand-made' MASCODEC UseOption from the platform files and replace it...

Remove the 'hand-made' MASCODEC UseOption from the platform files and replace it with other options which automatically parsed from features.txt. Also clean up some outdated left-overs and add some missing information (e.g. be more accurate in the config file section). Try to use the most appropriate features - masd and/or masf depending on their characteristics, large_plugin_buffer in the jpegviewer chapter as this is the restricting factor etc.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@21426 a1c6a512-1295-4272-9138-f99709370657