Add support for /deep/ combinator

[antonmoiseev]

Right now csso completes with exception trying to read a block like this:

* /deep/ .icon-star-empty:before {
  content: "\e60e";
}

Error:

/usr/local/lib/node_modules/csso/lib/gonzales.cssp.node.js:399
        throw new Error('Please check the validity of the CSS block starting f
              ^
Error: Please check the validity of the CSS block starting from the line #113
    at throwError (/usr/local/lib/node_modules/csso/lib/gonzales.cssp.node.js:399:15)
    at checkStylesheet (/usr/local/lib/node_modules/csso/lib/gonzales.cssp.node.js:1921:22)
    at Object.CSSPRules.stylesheet (/usr/local/lib/node_modules/csso/lib/gonzales.cssp.node.js:365:40)
    at _getAST (/usr/local/lib/node_modules/csso/lib/gonzales.cssp.node.js:409:38)
    at exports.srcToCSSP (/usr/local/lib/node_modules/csso/lib/gonzales.cssp.node.js:2287:16)
    at Object.exports.srcToCSSP (/usr/local/lib/node_modules/csso/lib/gonzales.cssp.node.js:2292:16)
    at exports.parse (/usr/local/lib/node_modules/csso/lib/cssoapi.js:7:21)
    at Object.exports.justDoIt (/usr/local/lib/node_modules/csso/lib/cssoapi.js:21:41)
    at Object.<anonymous> (/usr/local/lib/node_modules/csso/lib/csso.js:35:45)
    at Module._compile (module.js:456:26)

[spalger]

👍

[JosefJezek]

👍

[robdodson]

👍 We're using csso in the Polymer yeoman generator so I think I may have to remove it if I can't get this to work :(

[yadomi]

👍