clang-format

[bernhardmgruber]

• added a .clang-format file, based on the one suggested for alpaka: Improve clang-format support alpaka#781
• formatted whole codebase
• enabled trailing return types in clang-tidy and applied fix

[psychocoderHPC]

We need to document in the readme or contribution the command you need to use to format all files.

[bernhardmgruber]

Shouldn't that be obvious by the existance of the .clang-format file?

Otherwise, what would you prefer? Creating a new contributing.md, add it to readme.md, where there is no developer related content, or install.md where the build instructions are?

As for the command, that depends a lot on what shell and operating system you use. I think a developer should find this information for themselves on the web.

[psychocoderHPC]

Shouldn't that be obvious by the existence of the .clang-format file?

No it is not because the command is not simply clang-format, do not assume that someone knows a special tool.

Otherwise, what would you prefer? Creating a new contributing.md, add it to readme.md, where there is no developer related content, or install.md where the build instructions are?

I see we do not have such a file, so I suggest to create it and link it in README.md too.

As for the command, that depends a lot on what shell and operating system you use.

You can provide it for linux and windows. MAC should be equal to windows.

I think a developer should find this information for themselves on the web.

You can provide a link to the documentation but give them a copy past line too.

[bernhardmgruber]

I added a CONTRIBUTING.md and described briefly how to format.

[psychocoderHPC]

Note: We will take this code style for now. It could be we need to update this file again after we agreed for a common style file in ComputationalRadiationPhysics/contributing#33