Create README.md

Provides basic information on the GitHub page.
Cleanup: convert tabs to 8 spaces in the JS file.
Use HTTPS for all referenced URLs that support it.
Bug 25923 - Clarify MediaKeySystemOptions member names and descriptions.
Bug 25923 - Extract checking of individual MediaKeySystemOptions configurations into a separate algorithm.
Bug 25923 - Provide more detailed steps for checking audioType and videoType.

The new steps are similar to the removed isTypeSupported() algorithm.
Bug 25923 - Use in-algorithm variables to check combinations of all dictionary items.
Bug 25923 - Extract processing of the content type and capability to a separate algorithm.
Bug 25923 - Support arrays of initData types and audio/video types-capability pairs.
Bug 25923 - Check audio and video capabilities last since the other dictionary members may affect whether they are supported.
Bug 25923 - Rename "capability" to "robustness".

This more accurately reflects its purpose and avoids confusion with other uses.
Bug 25923 - Expose the supported combination from MediaKeySystemAccess.
Bug 25923 - Update Clear Key's MediaKeySystemOptions behavior.
Bug 25923 - Improve naming and other cleanup.
Bug 25923 - Remove obsolete isTypeSupported() text and references to this bug.
Remove "title" attributes from all <var> elements.