First pass at WebGL 2.0 specification.

This is not even close to complete. Please consider it a work
in progress.

- Make a new latest/2.0 directory. Copied the contents from 1.0.
- Update the boilerplate.
- Update the references. Add pointers to GLES 3.0 and GLSL ES 2.0.
- Start with some small spec content changes.
- Mark areas that need update.
- New CSS style for editor's notes.
Create new base interfaces for WebGL Contexts

- Also update context creation text to describe how to get a 2.0 context.
Update webgl.idl for WebGL 2.0 spec modifications.
Describe copyBufferSubData.

(also added a new class name to highlight definitions new in 3.0)
Update webgl.idl for copyBufferSubData.
Remove everything that is common with WebGL 1.0

After discussion with Ken, we agreed that for now the WebGL 2.0
spec should start by only describing the differences from WebGL 1.0.

At the moment, most sections are placeholders. New content includes:

- two new enums in "Types"
- new attribute in WebGLContextAttributes
- getParameter types under "Setting and getting state"
- everything from the previous commits
SAMPLER_BINDING should be a WebGLSampler
Typo in FRAMEBUFFER. Correct the return type for some values of getParameter.
PIXEL_UNPACK_BUFFER_BINDING should be a WebGLBuffer.
VERTEX_ARRAY_BINDING needs a WebGLVertexArray.
WebGLVertexArray -> WebGLVertexArrayObject
Add the new enums for WebGL 2.0 from the list in gl3.h
Add WebGLQueryObject, WebGLSampler and WebGLVertexArrayObject
Add WebGL2 API entry points (content provided by Ken Russell)

- also move the enums into the WebGL2 base class.
Escape sequence types in IDL otherwise HTML is wrong and our extraction tool barfs.
Extracted definitions for Framebuffer section.
Rename webgl.idl to webgl2.idl

Also remove latest/index.html in preparation for landing page that
will direct to 1.0 or 2.0.
Somehow I managed to not commit these files in the previous change.
Add the remainder of the 2.0 API entrance points (provided by Ken)
Add a temporary redirect to the 1.0 spec. We'll replace this with a real landing page soon.