Bug fixes and CMake build and versioning improvements
You can now build cppgraphqlgen using the add_subdirectory command in CMake as an alternative to importing it with find_package from an external installation.
The version number of the project was getting out of sync with the release tags in git, so now it keeps track of the project version number in a separate version.txt file. Anytime there's a new release tag with a greater version number, the CMake configuration should bump the version it uses in version.txt up to match. This should make it so clones of the git repo automatically stay up to date with released version numbers, and worst case if I forget to bump version.txt before tagging a release, consumers building from a non-git source archive should be at most 1 version number behind since it will have been last updated when building the prior version.