Fix spelling errors and grammar in documentation and messages

CHANGELOG.md

doc/doxygen/Doxyfile.in

lib/icu_compress/cmp_icu.c

programs/cmp_io.c

test/bench/leon3_grtimer.c

test/bench/leon3_timers.h

test/bench/timefn.c

test/cmp_icu/test_cmp_icu.c

test/tools/generate_test_runner.rb