Do not mark functions in header files as 'static'.

[hannesbrandt]

Do not mark functions in header files as 'static'.

Analogous to cburstedde/libsc#226, this PR removes the 'static' keyword from inline functions in p4est's .h files.

[cburstedde]

Thanks! If you'd remove the 'unused' doxygen special comments, some warnings may show up when building the documentation. Would you be able to fix the worst of those that pop up?

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# Do not mark functions in header files as 'static'.

[hannesbrandt]

I've removed the @unused@ for the inline functions and updated their documentation. There are also some functions affected by this PR that did not have the @unused@ in their documentation and are currently undocumented, which leads to a doxygen warning. Should I add documentation for these functions as well?

[cburstedde]

I've removed the ***@***.***@` for the inline functions and updated their documentation. There are also some functions affected by this PR that did not have the ***@***.***@` in their documentation and are currently undocumented, which leads to a doxygen warning. Should I add documentation for these functions as well?

If you can that would be awesome.

[cburstedde]

Thanks so much!