Change algorithm to mimic bash more closely. Remove break_cmdline_into_words() and merge the code into parse_cmdline(). Now does not strip first word, because bash also does not in COMP_WORDS. Now 'cmd foo ^ bar' works (becomes ['cmd', 'foo', '', 'bar']. In short, parse_cmdline() should [be able to] produce the equivalent of bash's COMP_WORDS and COMP_CWORD.
parse_cmdline(): Add option to preserve quotes, like bash. For example, 'cmd "foo bar"' becomes ['cmd', '"foo bar"']. Although this is not enabled by default.