add Font:getGlyphPosition

[thethethetheraven]

this implements Font:getGlyphPosition as outlined in issue #1021.

[thethethetheraven]

demo:

local utf8 = require "utf8"

local text = "hello, this is a program that uses Font:getGlyphPosition()."
local font = love.graphics.newFont(30)

local i = 1

function love.load()
	love.keyboard.setKeyRepeat(true)
end

function love.keypressed(k)
	if k == "right" then
		i = i + 1
	elseif k == "left" then
		i = i - 1
	end
	i = math.max(math.min(i, utf8.len(text)), 1)
end

function love.draw()
	love.graphics.setFont(font)
	love.graphics.setColor(0.8, 0.5, 0.8)
	love.graphics.rectangle("fill", font:getGlyphPosition(i, text, 400))
	love.graphics.setColor(1, 1, 1)
	love.graphics.printf(text, 0, 0, 400)
end