New front matter
Use some better names

c -> id, s -> s-map, st -> state
More naming improvements

$ -> stream, g -> goal
Make stream-to-seq polymorphic
Improvements around walk*
Use an explicit add-substitution

(assoc nil :key :val) returns {:key :val}, so it's not suitable for
extending the substitution alone. Add a function which checks for nil
first; a nil substitution means we've reached a contradiction somewhere
upstream, and we shouldn't be adding anything to it.
Move equality check to the unify function
Fix docs
Make sequences use 'dot' sigil instead of LCons