explore abr_range() and abr_rex()
scaffold abr_range_next
add abr_range() specs
accept escapes in abr_range()
implement basic abr_n_rex()
group quantifier parsing/extraction
let min/max default to -1
generify abr_p_string_to_s() (string/range/rex)
introduce rex abr_parser type
take "all children" approach for abr_decompose_rex
add spec for abr_range and ^
add spec for abr_range and \^
define ABR_STRING, ABR_SEQ, ...
use enum abr_p_type instead of defines
accept abr_rex("a+")
deal with abr_rex("ab+") (still have to reverse)
upgrade flutil and use flu_list_to_array_r()
add spec for abr_n_rex()
accept abr_rex("ab+c")
introduce abr_error

to detail invalid parser definitions