changed name treeof_datafiles to dirtree_datafiles
moved the bulk of function setup_filetable to a new method of
dirtree_datafiles; but retained a wrapper so that the function may
still be called.
changed name treeof_datafiles to dirtree_datafiles
Improved __repr__, etc. in filters.
New member functions for basic_datafiles, which I expect that all future
derived classes will implement.
Extensive changes to dirtree_datafiles class (renamed from treeof_datafiles).
Notably, the bulk of the former setup_filetable function has been
reimplemented as a method here.  The same was done with the never-used function
clear_filetable..  And there is a new method, check_filespec
(making them all methods of this class allows re-use of data such as the
files list, for possible efficiency.  And it's a more logical organization.)
new functiondiagnostics_menu, as described in the Python API in the design
document.  For now you can only get AMWG out of it.