Before you could choose between Merlin-style and generic. Now
there's a combo box that lets you choose Merlin, cc65, or
"common", the latter being used for 64tass.
Once upon a time, symbol files and extension scripts could only be
defined in the RuntimeData directory, so having the documentation
there made sense. Since both of these things can now be defined in
project directories, the documentation belongs in the manual.
(issue #27)
