gagolews/stringi: stringi_1.1.6

CHANGELOG: * [WINDOWS SPECIFIC] #270: Strings marked with `latin1` encoding are now converted internally to UTF-8 using the WINDOWS-1252 codec. This fixes problems with - among others - displaying the Euro sign. * [NEW FEATURE] #263: Add support for custom rule-based break iteration, see `?stri_opts_brkiter`. * [NEW FEATURE] #267: `omit_na=TRUE` in `stri_sub<-` now ignores missing values in any of the arguments provided. * [BUGFIX] fixed unPROTECTed variable names and stack imbalances as reported by rch