Unify dev/examples-to-*.el files

[basil-conto]

This unifies the somewhat overlapping and interpreted dev/examples-to-*.el files into a single byte-compiled harness dev/dash-defs.el (suggestions for a better name are always welcome).

• dev/examples-to-docs.el:

• dev/examples-to-info.el:

• dev/examples-to-tests.el: Delete files. Combine features into...

• dev/dash-defs.el: ...this new file.

• Makefile:

• dev/examples.el: Simplify accordingly. (approx-equal): Move definition to dev/dash-defs.el, where it's generated. (Predicates, Indexing, Threading macros, Binding) (Destructive operations, Function combinators): Add missing or fix existing docstrings.

• dash-template.texi (Functions):

• readme-template.md (Functions): Remove gratuitous newlines.

• README.md:

• dash.texi: Regenerate docs.

[basil-conto]

I plan to merge this in a week or so if there are no comments/objections before then.