meson: improve summary() printout

Pass bool_yn kwarg to summary() to make it
print boolean arguments as nice coloured YES/NO
instead of true/false.

We can also pass multiple arguments like a bool
and a disabled_reason string. In meson 0.54 these
can be printed on one line if we set the line_sep
kwarg. In meson 0.53 these will always be printed
on two lines (and it will warn about the line_sep
arg), so only pass two args if docs are disabled
and otherwise just pass one arg, so we don't end
up with an ugly empty line with meson 0.53.
4 jobs for meson-summary-improvements in 5 minutes and 39 seconds (queued for 11 seconds)
Status Job ID Name Coverage
  Build
passed #1926867
debian sid

00:00:46

passed #1926870
docker windows 1809
msys2

00:04:51

passed #1926868
docker windows 1809
vs2017 amd64

00:02:16

passed #1926869
docker windows 1809
vs2017 x86

00:02:13