Replace use of deprecated APIs in C tests

[edwardalee]

This PR is a companion to 353 in reactor-c, which removes deprecated API macros originally used in reaction bodies in the C target.

[edwardalee]

This PR is ready for review. There is a companion PR in reactor-c that requires a further companion review in the benchmarks repo in order to get all tests to pass.

[erlingrj]

Looks good!

[lhstrh]

Looks like the right thing to do. It implies that the next version should be 1.0.0, not 0.7.0...

[edwardalee]

Yes, I'm also focused on a much-needed code cleanup pass. I could use some help figuring out how to get Doxygen to give a reasonable layout of the documentation web pages. The pages themselves are getting much better, but the layout is absurd.

[lhstrh]

@arengarajan99 worked on this a while ago but hit roadblocks because the code itself wasn't well organized. That situation has improved a lot since then, so I'm curious whether his attempt could be reinvigorated.

On the versioning: I think that we should plan a 1.0 version more carefully and release it only once we can confidently consider it stable... We can choose to strictly follow semantic versioning rules from v1.0 and on...