A couple of issues with compiler.rst

[DimitrisJim]

There's a couple of issues I've found, I'm creating this issue to see if some of them were intentional.

I'm not sure if the following were intentional or not:

• Many of the functions and filenames aren't highlighted in any way. This fact leads to, at least in my opinion, harder to read sentences. Backticks and :file: directives could be used.
• The C snippet isn't highlighted with a code-block directive.
• A couple of macros contain the type for the arguments they receive, others don't.

Some changes that need to be made:

• NEW_BLOCK was removed in 3.6, if I'm not mistaken.
• PyEval_EvalFrameEx was changed with PEP 523, PyEval_EvalFrameDefault contains the big switch as mentioned.

I've probably missed some other functions that were renamed/tweaked, I'll keep checking to see if anything else is needed.

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All in all, this file is a really useful resource for anyone interested in the CPython compiler; it should be polished up and, if possible, linked in exploring.rst in some way.

[brettcannon]

All of the formatting issues are because I originally wrote that doc as an informational PEP before I wrote the original version of the devguide (which makes me realize how much I write 😅 ). So fixing the formatting of the page to utilize reST better is totally fine.