[Bind] Added documentation files for OpenGL ES
[Bind] Process documentation from subdirectories

Instead of using xslt, we now process the documentation in code. This
allows us to fix mismatches from e.g. invalid parameter names that
sometimes creep in the specs.
[Bind] Concatenate multiline documentation
[Bind] Merge GL2 and GL4 documentation into one
[Bind] Use DocumentationParameter instead of KeyValuePair
[Bind] Remove xmlns to simplify xpath processing
[Compatibility] Don't generate xml documentation
[Bind] Do not skip parameters in documentation

Multiple parameters may share a single description. The DocProcessor
will now correctly generate DocumentationParameters for each of them.
[Bind] Add NoIndent option to BindStreamWriter
[Bind] More aggressive trimming of documentation strings
[Bind] Propagate ComputeSize attribute in cloned Parameters
[Bind] Make documentation output closer to previous xslt implementation
[Bind] Move documentation generation to DocProcessor class

This de-duplicates a large amount of code that is shared between the
various ISpecWriter implementations.
[Bind] Corrected CSharpSpecWriter output and warning messages

CSharpSpecWriter now correctly outputs doc summaries on ARB_imaging
functions that do not have a version/deprecation string. Additionally,
it no longer warns about documentation parameter mismatches for
parameters matching C# keywords.
Merge branch 'es_docs' into develop