fix package build not using new lexical features

[step-]

Files gtkdialog_lexer.c and gtkdialog_parser.[ch] aren't source files; flex and bison generate these files from their corresponding .l and .y sources as part of making the target. Leaving the .[ch] files in the repo can lead to a bad build. If the repo is downloaded from github to build from sources, all files share the same timestamp, therefore the lexer and parser are built from the existing - and possibly old - .[ch] files instead of from [.ly] files as they should be.

[step-]

@01micko, what etiquette do you want me to follow as regards commits to this repo? You hinted I could merge PRs, did you mean it or do you want to merge?

[01micko]

@01micko, what etiquette do you want me to follow as regards commits to this repo? You hinted I could merge PRs, did you mean it or do you want to merge?

Normally we issue PR and request a review, and merge it our selves when reviews are satisfied. I'll merge this one.

[dimkr]

Something is wrong with the autotools build of 0.8.5, still not sure what causes this:

gtkdialog.c:48:10: fatal error: gtkdialog_parser.h: No such file or directory
   48 | #include "gtkdialog_parser.h"
      |          ^~~~~~~~~~~~~~~~~~~~
compilation terminated.
make: *** [Makefile:549: gtkdialog.o] Error 1

[step-]

See #147