Merging lots of stuff in from development branch for 1.3.0 release.
* Added `:default' feature to `map' constructor macro.
* Some new modify macros: `includef' (replaces `adjoinf'), `excludef'
(replaces `removef'), `intersectf', `imagef', `composef'. `reduce' now
works on maps.
* Added operations:
() `split' (two-valued `filter')
() `splice' (splice a seq into another seq)
() `appendf' and `prependf' (seq concat-and-assign)
() `tuple-key-name' (new export)
Also, changed `concat' from binary to n-ary.
* Made the methods for `sort' and `stable-sort' on CL sequences copy the
sequence first, so these are now functional operations -- consistent with
FSet semantics, but not with their CL definitions. (In practice the
sequence usually has to be copied anyway; and you can always call `cl:sort'
explicitly if you don't want it to be copied.)
* Made (convert 'vector seq) always return a simple-vector, instead of
figuring out dynamically whether to return a string (which fails on the
empty seq, duh). Added (convert 'string seq) that always returns a string
(errors if it can't).
* New, experimental type `list-relation'. Various other improvements to