cairo - cairo graphics engine

`local cairo = require'cairo'`

A lightweight ffi binding of the cairo graphics library with the following features:

cairo types have associated methods, so you can use context:paint() instead of cairo.cairo_paint(context)
pointers to objects for which cairo holds no references are bound to Lua's garbage collector to prevent leaks
ref-counted objects have a free() method that checks ref. count and a destroy() method that doesn't.
functions that work with char* are made to accept/return Lua strings.
output buffers are optional - if not passed on as arguments, temporary buffers are allocated instead; the values in the buffers are then returned as multiple return values, such as in context:clip_extents([dx1][,dy1][,dx2[,dy2]) -> x1, y1, x2, y2, where dx1 etc. are double[1] buffers.
the included binary is built with support for in-memory surfaces, recording surfaces, ps surfaces, pdf surfaces, svg surfaces, win32 surfaces, win32 fonts and freetype fonts.

See the cairo manual for the function list, remembering that method call style is available for them.

Additional wrappers are provided for completeness:

`cr:quad_curve_to(x1, y1, x2, y2)`	add a quad bezier to the current path
`cr:rel_quad_curve_to(x1, y1, x2, y2)`	add a relative quad bezier to the current path
`cr:circle(cx, cy, r)`	add a circle to the current path
`cr:ellipse(cx, cy, rx, ry)`	add an ellipse to the current path
`cr:skew(ax, ay)`	skew current matrix
`cr:rotate_around(cx, cy, angle)`	rotate current matrix around point
`cr:safe_transform(mt)`	transform current matrix if possible
`mt:transform(with_mt) -> mt`	transform matrix with other matrix
`mt:invertible() -> true\|false`	is matrix invertible?
`mt:safe_transform(with_mt)`	transform matrix if possible
`mt:skew(ax, ay)`	skew matrix
`mt:rotate_around(cx, cy, angle)`	rotate matrix around point
`surface:apply_alpha(alpha)`	make surface transparent