change default command of make
do not drop into repl when make is called without arguments
update README
add vector-map, vector-for-each, string-map, string-for-each
fix #6
Revert "[bugfix] do not fuse end-of-page block into other blocks"

This reverts commit 5656590fa06023de76ef366451376156ee5bdec3.
add freed object counter
[gc][bugfix] sweeping failed when the heap gets completely
exhausted (i.e. all blocks' size are zero)
Merge pull request #7 from zeptometer/control-features

add vector-map, vector-for-each, string-map, string-for-each
update readme
cosmetic changes
calloc should take size_t
rewrite pic_type_repr
fix logic flaw in GC
remove a field for debug of union header
set bitfield to union header.mark
GC_STRESS off by default
macroexpand_list supports any kind of improper list
exprs during macroexpansion may have syntactic-closure in the tail position
remove old debug prints