Add `invert` arg to `stri_locate_*`

[gagolews]

invert_match {stringr}  R Documentation
Switch location of matches to location of non-matches.

Description

Invert a matrix of match locations to match the opposite of what was previously matched.

Usage

  invert_match(loc)
Arguments

loc 
matrix of match locations, as from str_locate_all

Value

numeric match giving locations of non-matches

cf. https://github.com/hadley/stringr/issues/50

[gagolews]

related to #48