UNFINISHED: started porting to CCL, i.e. Clozure Common Lisp
added some SBCL-specific optimizations
removed broken :weakness and :weak support from thash-table
new file doc/introduction.md
updated README.md and doc/benchmark.md
renamed util/pqueue.lisp -> util/bheap.lisp
refactored (defclass tvar ...) -> (defstruct tvar ...)
refactored (defclass tlog ...) -> (defstruct tlog ...)
updated benchmark