This adds the concept of label annotations. The primary driver of
the feature is the desire to note that sometimes you know what a
thing is, but sometimes you're just taking an educated guess.
Instead of writing "high_score_maybe", you can now write "high_score?",
which is more compact and consistent. The annotations are stripped
off when generating source code, making them similar to Notes.
I also created a "Generated" annotation for the labels that are
synthesized by the address table formatter, but don't modify the
label for them, because there's not much need to remind the user
that "T1234" was generated by algorithm.
This also lays some of the groundwork for non-unique labels.
SourceGen creates "auto" labels when it finds a reference to an
address that doesn't have a label associated with it. The label for
address $1234 would be "L1234". This change allows the project to
specify alternative label naming conventions, annotating them with
information from the cross-reference data. For example, a subroutine
entry point (i.e. the target of a JSR) would be "S_1234". (The
underscore was added to avoid confusion when an annotation letter
is the same as a hex digit.)
Also, tweaked the way the preferred clipboard line format is stored
in the settings file (was an integer, now an enumeration string).
