calc 2.16.1.0 release

[lcn2]

The following are the changes in this release:

Added a new `.clang-format` file as the basis for using the
`clang-format(1)` tool to format calc source in a consistent way.
This code re-formatting will make it easier to work in calc v3 code
changes in the future by making the calc source much more consistent.

Removed `.clang-format` exclusion from `.gitignore`.

Modified `func.c` to prevent the `clang-format(1)` tool from formatting
the `builtins[]` table that builtin make rule in `help/Makefile` uses to
format the `help/builtin` file.  We can live with the `builtins[]`
table as it is today, for now.

Add `make clang-format` make rule to top level `Makefile` and
to the `custom/Makefile`.

Reformatted C code as per the `clang-format(1)` and the
`.clang-format` file: using the `make clang-format` make rule.

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This discussion was created from the release calc 2.16.1.0 release.

[lcn2]

Quick update

It goes well with calc version 2.16.0.3, and then with calc version 2.16.1.0:

• we HIGHLY RECOMMEND UPGRADING TO calc version 2.16.1.0

We will use that code as the basis for starting the calc v2/calc v3 fork process as outlined in the top comment of this issue.

Help requested

We need to encourage the maintainers of Extra Packages for Enterprise Linux EPEL calc to update to this version. Any help folks can give to help accomplish this would be greatly appreciated.

Also, @pmetzger, if you could update Macports and/or homebrew for calc, that would be most appreciated.