Comparators, #1, untested

It is easier to test once ranges are implemented.
Internal changes, rematch -> re_match, return match, add re_place
Rewamp string utils, include stringr

R string operations are just ridiculous, especially strsplit.
Fix several basic comparator bugs
Fix cmp for op = "", op = "="

These might be coming from comparators.
Ranges

Also, tests for comparators. Some mall bits are still missing:
gtr, ltr, max_satisfying, comparison operators, sorting, maybe more.