Support `unicode-range` syntax

[yisibl]

@font-face {
    font-family: 'Ampersand';
    src: local('Times New Roman');
    unicode-range: U+26;               /* single codepoint */
    unicode-range: u+26;
    unicode-range: U+0-7F;
    unicode-range: U+0025-00FF;        /* codepoint range */
    unicode-range: U+4??;              /* wildcard range */
    unicode-range: U+0025-00FF, U+4??; /* multiple values */
    unicode-range: U+A5, U+4E00-9FFF, U+30??, U+FF00-FF9F; /* multiple values */
    unicode-range: U+????;
    unicode-range: U+??????;
    unicode-range: U+12;
    unicode-range: U+12e112;
    unicode-range: U+1e1ee1;
    unicode-range: U+1e1ee?;
    unicode-range: U+12-13;
}

[devongovett]

Implemented in the above commit. Also optimizes ranges to use the question mark shorthand where possible.

The following examples listed above are not valid, however. A maximum of 5 question marks are allowed, and values must be in the range 0 - U+10ffff.

unicode-range: U+??????;
unicode-range: U+12e112;
unicode-range: U+1e1ee1;
unicode-range: U+1e1ee?;