Add version flag

[jkhoogland]

Adds a --version,-v flag to show the version of application.

• version is pulled the cmake variablePROJECT_VERSION set in CMakeLists.txt.

Fixes cmake build on macos; libyaml was not properly included.

[lawmurray]

Thanks @jkhoogland, will review.

Linking #56 as related on the libyaml issue. The idea there is to use system packages where available (e.g. libyaml might be installed from Homebrew on macos) and only use the submodules in contrib if they are not available.

[lawmurray]

Thanks again for this @jkhoogland . The --version feature works for me, so that's great. The libyaml changes are not working for me on Ubuntu 24.04, however. It's not finding the system-installed libyaml (from the libyaml-dev package) and deferring to the submodule.

If you're in a position to test that change some more on Linux, then I'd appreciate that. If not, can we just remove the libyaml change from this pull request to handle it separately, and I can merge the --version changes?

[jkhoogland]

From what I can tell both on macos and linux (arch) the standard package for libyaml does not contain any cmake config files for libyaml. So find_package will error out.

I add a switch to only do this on macos if that makes the PR acceptable?

On archlinux:

pacman -Ql libyaml

gives

libyaml /usr/
libyaml /usr/include/
libyaml /usr/include/yaml.h
libyaml /usr/lib/
libyaml /usr/lib/libyaml-0.so.2
libyaml /usr/lib/libyaml-0.so.2.0.9
libyaml /usr/lib/libyaml.so
libyaml /usr/lib/pkgconfig/
libyaml /usr/lib/pkgconfig/yaml-0.1.pc
libyaml /usr/share/
libyaml /usr/share/licenses/
libyaml /usr/share/licenses/libyaml/
libyaml /usr/share/licenses/libyaml/LICENSE

[jkhoogland]

I made the build of contrib/libyaml optional.

Use -DBUILD_YAML=ON to add the local build of libyaml.

[lawmurray]

Looks good @jkhoogland, that setup for libyaml seems sensible to me. Thanks for the work on this one and for contributing to Doxide!

Closes #61.