Use separate type for identifiers.
Use Filename.concat.
Allow SF path to be given on configuration file.
Don't read configuration file if it doesn't exist.
Improve CL option reading and error messages.
Fix parsing of test tags.

Really sad that Str's interface is not functional...
Add line breaks to error messages.
Fix command line argument reading.
Implement run_test.
Allow functional_extensionality axiom.

Still need to allow axioms to be allowed on a per-exercise basis.
Update TODO file.