implemented completely
call symbol_rename as much as possible
macro transformer should never return macro objects
no need to handle set!/if/begin syntaces at macroexpansion stage
cleanup
Merge branch 'refactor-macroexpand'
implemented simple backtrace
Merge branch 'backtrace'
add user-defined data type API
Merge branch 'data-type'
refactor pic_gensym
refactor native_stack_length
fix #84
Merge branch 'issue-84'
add fixed-arity pic_values function
add pic_assert_type
add pic_data_type_p
cleanup
initial regexp support
update readme