Add meson option to force color output when output is not tty

meson disables color output if stdout is not tty, as below:

mesonbuild/mlog.py:

colorize_console = platform.system().lower() != 'windows' and os.isatty(sys.stdout.fileno()) and \ os.environ.get('TERM') != 'dumb'

This works good normally. But colored log files are needed for sharing log across html email / link ( to pin point the exact areas of concern ( red / yellow warnings etc ). Colored output is much faster to debug than plain text. Screenshot is a very limiting option. An option to meson ( similar to ls --color=always ) should help here.

Example color log file:

root@vbox:~# apt-get install aha

set colorize_console = True in mesonbuild/mlog.py

user@vbox:/local/meson/source$ meson ../build | aha > ../build/log.html