Try flipping RTL text (#472)

[mapmeld]

I was interested in right-to-left labels for my project, so I tried out a couple of things. This code essentially 'flips' any RTL text and multi-word phrases.

It unfortunately only works on bidirectional text if there is a space between LTR and RTL words, so Casablanca shows up wrong. It's tough for me to know if the rest of the Arabic labels are written properly, but I might be breaking connections between letters by flipping it like this.

[mikemorris]

So, even after flipping the Arabic labels will still not be rendered properly, because complex text shaping has not yet been implemented.

For displaying RTL/LTR text properly, we should use the Unicode Bidi Algorithm.

Twitter ported this and some other bits or i18n logic from ICU, which might be a good place to start.

Refs #472

[jfirebaugh]

@mapmeld, thanks for the contribution. I think we are going to wait until we have time to implement a more complete solution along the lines of what @mikemorris suggests. Of course if you want to dive into that you'd be very welcome!