implement sub-pixel RGBA text antialiasing

Squashed commit of the following:

commit a7ac0a293add70df1451c8dfa536c85fefc6f23a
Author: William Light <wrl@illest.net>
Date:   Sat May 18 23:52:04 2013 +0200

    remove pt sans

commit 8a8ad9169a225a5a31103ca14e36bedef0b97e00
Author: William Light <wrl@illest.net>
Date:   Sat May 18 23:50:35 2013 +0200

    remove text-alpha shader

commit f4408966bba48323153de6bec693f79f15cd56da
Author: William Light <wrl@illest.net>
Date:   Sat May 18 23:39:49 2013 +0200

    fix glyph positioning

commit cba5bb82c1825a5cf610d91203ebf9a7bd96ecd0
Author: William Light <wrl@illest.net>
Date:   Sat May 18 22:46:24 2013 +0200

    use rtb_utf32_t instead of char32_t

commit dd119b6b68c71d2da49268de544d0a2c2ba1912e
Author: William Light <wrl@illest.net>
Date:   Sat May 18 20:21:46 2013 +0200

    serious fixes to LCD filtering

commit 7111ad510636e67bd1103dc33cd1fc4415019251
Author: William Light <wrl@illest.net>
Date:   Sat May 18 18:45:55 2013 +0200

    first crack at text LCD filtering