use register_core_symbol macro to initialize pic_state
[xhash] use strdup if possible
[xhash] cleanpu
add global identifier table
add core syntaces in pic_open
add xlen/xcapa member to pic_senv
debug prints for macroexpand
add missing core symbol registration
add 'define-macro' core syntax
save macro procesures in each syntax object
replace old macroexpand facility with new renamer implementation