Get version out of header files

[lunacd]

I'm not a huge fan of putting version information in header files as it pessimizes build caching in general, though keeping feature parity across CMake and meson is more important for this PR to land. A followon PR to consider another approach would be interesting to me. Eventually.

Originally posted by @bretbrownjr in #82 (comment)

[bretbrownjr]

Other options:

• Version info in a config file
• Version info hardcoded, but in a cpp file