generate an OpenCL C built-in functions dictionary

[bashbaug]

Possible fix for #1214

This PR generalizes the script used to generate OpenCL C feature dictionaries from #1212 so it can be used for other types of dictionaries also.

Then:

1. It adds a list of OpenCL C built-in functions and uses the script to generate a dictionary for them.
2. Replaces the built-in functions with hard-coded unicode zero-width spaces with the asciidoctor attributes instead.

I believe this fixes the issue.

A few additional notes:

• I've only added the built-in functions with the hard-coded zero-width spaces. If desired, we could add additional built-in functions, also.
• I haven't included any formatting in the generated built-in functions dictionary because some functions use bold formatting and other functions use monospace formatting. We ought to unify this at some point.

I've tried copy-pasting the function names from the HTML spec with both Chrome and FireFox and they both seem to work fine. I'm able to copy-paste the function names from the PDF spec, also.

[bashbaug]

I found a few formatting issues I need to fix. Converting to draft.

[bashbaug]

The formatting issue is fixed, so this is now ready to go.