Let's make line-number tests namespace specific
New `user` directory starts with parse error tests.
Forgot to update line numbers
Deprecation messages
Add directions to issue tracker (and guide) for parse exceptions
Moved another semi-sweet validation over to new style
Added an arrow to throw parse exceptions.
Moved some files around.
Documented two new directories
Converted =contains=> to new error-handling
Tidying in advance of next change
Move all background-validation stuff into the parsing directories
Remove dead code.
* The form of a background-changer within a fact is now more flexible.
* Background can take a let-style list
Add doc for "background changers" + 2 new guides
Better error message
Watch out for left-hand sides that are lazyseqs instead of lists.
Little utility that allows either a singleton vector or sequence of args
Get rid of annoying output from `unfinished`