Window title font size parameterization request

[AlexJakeGreen]

I observe window title is written with a very tiny font. An attempt to increase org.gnome.desktop.interface/font-name leads to unproportional font rendered in other places.

I think it will be nice to expose the font size parameter in wcm.

https://github.com/soreau/pixdecor/blob/master/src/deco-theme.cpp#L206

[soreau]

I think this function might need adjusting.

[soreau]

@AlexJakeGreen Can you possibly test #27 and see if this fixes the issue here?

[soreau]

Closing this since #27 has been merged.