Improving text

[emhoracek]

@aepyornis added text, but as he noted in the code, the width seems buggy.

Multiplying number of characters by the font size doesn't work, because letter width varies considerably. In most fonts, "i" and "l" are much thinner than "w" or "m". So the word "mmmmm" is a lot longer than "lilli", even though those are both 5 letters. And I think the font-size in pixels is not quite the same as either width.

So, right now, placeImage works fine with text, but overlay looks really broken. :/

Not sure that right way to fix this, but it interfering with my solution to #19 so I'm going to try some things.

[emhoracek]

Fixed by 6203a22 :D