Enforce proper code formatting

[DusanJovic-NOAA]

This section of code does not look properly indented, which makes it hard to read and reason about it:

This is because in my editor tabs are displayed as 4 spaces. We should not use tabs in the source code.

To fix:

1. Replace all tabs with spaces in all source files.
2. Delete trailing spaces.
3. Use clang-format to uniformly and consistently reformat all source code.
4. Enforce proper formatting in CI

[edwardhartnett]

Agree.

We are using 4-spaces, no tabs. If you see anything else, feel free to correct.

I have never used clang-format. I would welcome a CI that demonstrates this in the CI.

[DusanJovic-NOAA]

I added .clang-fomat in this commit f32fb5d

And with those settings I ran it in the src directory on all source files, see this commit (ignoring whitespace changes)

Is this acceptable format/style?

I ran it locally on my laptop, I do not know how to integrate it in CI.

[edwardhartnett]

Yes, that looks great. Let's get your commits merged and I will put clang-format in the CI.

Thanks for this, it's really helpful. I'll suggest it for the netcdf-c repo.