add option to skip binary files

Fix skip binary and add tests

update semver notation for istextorbinary, this should fix the travis build on 0.6 and 0.8

drop support for node 0.6, 0.7 and 0.8 (gulp 3.2 only supports node >= 0.9)

code style
Merge skipBinary PR from @tcoopman

Conflicts:
	README.md
	test/main.js
Bump version to 0.4.0