Right now this mostly just includes (most importantly) undo/redo,
and less importantly smarter deletion and keyboard navigation.

Because changing the background colour of a textview for some reason
causes text selection not to show. This is a documented issue others
experience.

This code could be refactored a little now, but it works for the
elementary and HighContrast themes.

Because for some reason this would happen seemingly at random before.
No idea why. But I did test that it occurs during save, not read.

And it doesn't appear to happen anymore.

This is manually computed, because GTK is just complaining it doesn't support percentages.

Previously, the initial dark mode toggle would cause the default
settings to be saved, before font preferences ever loaded.

Closes #11

Moves the word count to the title bar subtitle.

v0.36, not v0.26

This checks the returned error code from `writeas` and skips the browser
opening if the status != 0.

Turned out I was saving the theme before I had a chance to read
the values saved from the last run.

Though there seems to be problems reading it back out.

Now supports multiple fonts and the caller can be written more naturally.

TODO ensure it is installed with the packaging.

Previously it gave this warning:

dpkg-source: warning: unknown information field 'Recommend' in input
data in package's section of control info file

I slipped on this one -- the correct font value for monospace posts is
"wrap" not "mono". "mono" is more for code or terminal output, not the
writing that users will do with this app.