This adds 2 missing functions: cairo_surface_set_device_scale and
cairo_surface_get_device_scale, and also requires cario 1.14 or newer.
This addresses the comments in #1083.
Improved Lua API (lua_read_parse has been removed in favour of the
conky_parse() Lua API call). The docs have been improved to reflect the
recent Lua API stuff as well. Introduced new Lua Cairo and Imlib2
bindings, which require the tolua++ tool. Fixed some other
miscellaneous doc related things.