Keep VERSION consistent to LibTrixi.jl/Project.toml

[benegee]

Addendum to #56 : Do we need and can we make sure that the versions in file VERSION and LibTrixi.jl/Project.toml agree?

[sloede]

Do we need

I think we do. Different versions of libtrixi and LibTrixi.jl would IMHO just be confusing to users. Although nobody would be prevented from manually updating their LibTrixi.jl code independently of the C code, I think we should keep the versions in sync to maintain a single API.

and can we make sure that the versions in file VERSION and LibTrixi.jl/Project.toml agree?

TBH, I don't see how we can do that automatically in a sane way. Populating Project.toml from VERSION would mean that LibTrixi.jl cannot be used standalone anymore. And the other way around seems very convoluted (ie, having the version defined in a subdirectory file).

I guess I would just write it down in the developer section of our docs that the version numbers need to be kept in sync manually.

[sloede]

I've been thinking about this a little more. One could consider that LibTrixi.jl is really the main software product here, and that everything else is just a means to use it, ie, by providing C and Fortran bindings. In that case, we could remove the VERSION file and have the existing trixi_version_xxx functions call corresponding functions in LibTrixi.jl (as opposed to having hard coded return values as they do now).

This would also resolve #57, since we could just rely on JuliaRegistrator and TagBot to do the release process for us.

[benegee]

Sounds reasonable, fine with me.