Add contrast ratio and relative luminescence functions in the HTMLCS utils. This allows potential testing in SC 1.4.3 and 1.4.6 for contrast ratio messages.
Add contrast ratio and relative luminescence functions in the HTMLCS utils.
This allows potential testing in SC 1.4.3 and 1.4.6 for contrast ratio messages.

daam/HTML_CodeSniffer,adelevie/HTML_CodeSniffer,telesma/HTML_CodeSniffer,lwright-sq/HTML_CodeSniffer,adelevie/HTML_CodeSniffer,squizlabs/HTML_CodeSniffer,telesma/HTML_CodeSniffer,daam/HTML_CodeSniffer,ironikart/HTML_CodeSniffer,lwright-sq/HTML_CodeSniffer,squizlabs/HTML_CodeSniffer,ironikart/HTML_CodeSniffer,telesma/HTML_CodeSniffer,squizlabs/HTML_CodeSniffer,daam/HTML_CodeSniffer,adelevie/HTML_CodeSniffer,ironikart/HTML_CodeSniffer,lwright-sq/HTML_CodeSniffer