Tag Patchwork v0.1.2, Compose v0.3.10 and Gadfly v0.3.10

These releases contain several fixes to Compose:

https://github.com/dcjones/Compose.jl/pull/86
https://github.com/dcjones/Compose.jl/pull/88
https://github.com/dcjones/Compose.jl/pull/98
https://github.com/dcjones/Compose.jl/pull/99
https://github.com/dcjones/Compose.jl/pull/94
(also a fix for pre-compilation in userimg.jl)

The Patchwork back-end
https://github.com/dcjones/Compose.jl/pull/89

and `writemime` methods for `Signal{Context}` and `Signal{Plot}` which use Patchwork.