Additional matchers

[mltsy]

Just wanted to start an issue with a few additional matchers that I've wished were available here for when I get a chance to implement some (mostly copies from chai-webdriver):

• .have.htmlClass(name)
• .have.attribute(name, value)
• .have.element(selector) or contain(selector) (?)
• .be.disabled()

[mltsy]

(oops value is already there - I was thinking of a WebdriverIO problem I had selecting by value - removing that one!) :)