Web updates

WebDriver 971ab897921b

Generalize protocol extension mechanism (#1177) The facilities offered for protocol extensions are intended to be used by both web standards and browser vendors. Prior to the application of this commit, the specification text inconsistently described these two distinct use cases [1]. The mechanism itself was biased towards the "browser vendor" use case because it required the specification of an "extension command prefix" which is not appropriate for all "web standards" use cases [2]. Explicitly describe both use cases in the informative text and generalize the normative text to better-support extensions by web standards. [1] [2]