update links to point at mapbox
fix compile with clang/libc++ on OS X (now default on OS X 10.9)
maintain support for gcc on OS X <= 10.8
bump to v0.8.3
Merge branch 'master' of github.com:developmentseed/node-blend into node-v0.10.x

Conflicts:
	wscript
skip webp tests for now since imagemagick is not likely going to have webp support