Add support for CSS unicode-range single_codepoint

[cbikar]

Right now, the caja CSS Lexer only supports actual ranges as a value in the unicode-range property, like "U+0025-00FF".
According to the specification (http://dev.w3.org/csswg/css-fonts-3/#composite-fonts) it is also possible to define a single code point, like "U+A5;"
However, the CSS Lexer expects a "-" in each unicode-range value and throws this exception:

com.google.caja.lexer.ParseException: http://www.example.org:1+165: Expected - not ,