Fixes for latest libuv
Use mrb_module_get
fixes negative nread
ditt
enable UV_TCP_IPV6ONLY on version 6
add mrb_module_get workaround for mruby 1.0.0
add libuv builder for non Windows
Merge pull request #20 from take-cheeze/libuv_improvement

mruby-1.0.0 support and libuv improvement.
always call close callback, free ref for GC