1) [input.lua] Pressing backspace while the cursor was at the beggining
of the text removed the first character. Fixed thanks to riidom.
2) [LÖVE 0.9] Use setLine(Width|Style) instead of setLine. Split
keyboard.pressed() into keyboard.pressed() and keyboard.textinput().
(see readme)
3) [utf8.lua] Add support for UTF-8 text editing. May still fail
spectacurlarly with invalid UTF-8 strings.
When clicked, Button() and Input() return the respective mouse button
constant ('l', 'r', 'm') instead of just true.
When activated by keyboard, Button() and Input() return 'return'.
Otherwise Button() and Input() return false.
