Replaced the regex-based transformation of CSS to XPath

The library now uses the Symfony CssSelector component, which supports
more cases than the custom logic used previously.
Closes #34
Skip `!important` attributes

Skips the properties when they are marked as `!important`, unless the new attribute is also `!important`. Fixes #57
Refactor specificity

Don't use a value, but compare the 3 values in a seperate class. And
don't add the order to the specificity, only use it when the specificity
is equal.
Don't ignore lock-file'
Merge branch 'stof-use_symfony_css_selector'
Bumped version
Merge branch 'patch-3' of github.com:barryvdh/CssToInlineStyles into barryvdh-patch-3
Updated changelog
Merge branch 'barryvdh-patch-3'
Bumped version
Merge branch 'master' into specificity

Conflicts:
	CssToInlineStyles.php
Use regex for specificity

And added getValues() (for easier testing) and changed to compareTo, in
line with the CssSelector component.
added unit tests
added composer autoloader to test bootstrap
Tweak match count
Cleanup
hhvm compatibility when specificities are equal
simplify test bootstrap
Tweak important detect

The $value is always an array, not a string. Implode them before checking, instead of skipping.
The earlier version did work a bit, bit had problems with multiple !important statements.
Merge pull request #62 from barryvdh/patch-4

Tweak important detect