Move async and defer properties to attributes.
Merge branch 'master' into move-async-defer-to-attributes. Little refactoring.

Resolve conflicts:
	src/CeesVanEgmond/Minify/Minify.php
	src/CeesVanEgmond/Minify/Providers/JavaScript.php
Tests passing. BaseProvider tags() and add() method refactoring. Prettifying tag output.
Merge pull request #57 from smgladkovskiy/move-async-defer-to-attributes

Move async and defer properties to attributes.