specl: -v doesn't change formatter, support -f for that.

* README.md (Command Line): Document change of meaning for
`--verbose`.
* specl/version.lua.in (M.opts): Default verbose to false.
(M["--help"]): Document changes to command line interface.
(M["--verbose"]): Don't change formatter, set verbose mode.
(M["-f"]): An alias for `--formatter`.
* specl/formatter/progress.lua, specl/formatter/report.lua
(footer): Only show the failure summary in verbose mode.
* GNUmakefile (specl_verbose_0): Pass `--verbose` to get failure
summary.
* specl/std.lua (process_args): Support short option arguments.
(specl_verbose_1): Additionally, switch to the report formatter.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>
refactor: encapsulate coloring into util.princ.

* specl/util.lua: Require "specl.color".
(M.princ, M.writc): Wrap ansicolor printing with princ, and
io.stdout:write with writc.
* specl/formatter/progress.lua, specl/formatter/report.lua:
Require "specl.util" instead of "specl.color".
Use princ and writc wrappers.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>