Manage project version with cmake

[K20shores]

This PR defines the version in the cmake project call. CMake will automatically parse the major, minor, and patch versions.

The version option defines a set of variables useable in the project, including configured files. For example, the major version is available using a mix of the project name (netCDF) and the part of the version you want: netCDF_VERSION_MAJOR

[CLAassistant]

All committers have signed the CLA.

[WardF]

Thanks @K20shores! There's a CLA button to click, too, that enables things on our end. It's an organizational thing, but clearly not across the entire organization XD.

[WardF]

Can you update configure.ac to change the variable name for consistency? As it stands, configure-based builds will fail to properly generate netcdf_meta.h since it will create NC_VERSION_x variables.

[K20shores]

@WardF I made that change. Again, if you'd prefer, I can use the variables that cmake sets to recreate the NC_* version variables; I figured that it's probably at least a little better to put the version in the project command so that cmake has the version information which can affect downstream projects.

[WardF]

Looks good @K20shores, thanks!