Set the async and defer optionnal
Switch to dev mode
Change the minifier for the js to use tedious/JShrink
#41 Add the onlyUrl, manually merge the develop branch
Merge branch 'master' into move-async-defer-to-attributes. Little refactoring.

Resolve conflicts:
	src/CeesVanEgmond/Minify/Minify.php
	src/CeesVanEgmond/Minify/Providers/JavaScript.php