autoconf/configure now prefers pkg-config to icu-config, as requested by Brian Ripley; see http://userguide.icu-project.org/howtouseicu
stri_enc_detect2 now has "NA" locale arg; stops searching if not UTF-*; moreover, only valid ASCII supersets are considered as candidates; stri_read_lines locale now defaults to NA; added fallback_encoding argument (now it more resembles readLines) - this fixes a BUG submitted by MB