Adds text which displays the number of matched and total items in the
top right corner of dmenu.

This patch adds translucency to the dmenu window, while keeping the text
in it opaque, just like the alpha patch for st.

XUngrabKey(), which is currently used in cleanup(), is not the right
counterpart to XGrabKeyboard(), which is used in grabkeyboard(),
called from main().

XUngrabKeyboard() is the function to use, as grabbing the whole
keyboard is different to grabbing individual keys.

With the current code the keyboard gets ungrabbed, as far as I can tell,
only by the final XCloseDisplay() in cleanup(), as the XUngrabKey()
there effectively does nothing.

Patch by Raymond Cole <rc@wolog.xyz>, thanks.

Original patch by Raymond Cole with some modifications, thanks!

previously drw_text would do the width calculations as if
invalid utf8 sequences were replaced with U+FFFD but would pass
the invalid utf8 sequence to xft to render where xft would just
cut it off at the first invalid byte.

this change makes invalid utf8 render as U+FFFD and avoids
sending invalid sequences to xft. the following can be used to
check the behavior before and after the patch:

	$ printf "0\xef1234567\ntest" | dmenu

Ref: https://lists.suckless.org/dev/2407/35646.html