Split up Actions workflow

[brentru]

This pull request splits the workflow from one file which builds and releases wippersnapper, into three files, as requested by @lorennorman.

Changes

• .github/workflows/build-clang-doxy.yml is run during a pull request and tests that we can build, lint and generate documentation for a PR submission.

We're using GH action's reusable workflow feature to avoid duplication of build steps within a release workflow:

• .github/workflows/release-caller.yml is the caller function which, upon new release of WipperSnapper, calls the build workflow (build-clang-doxy.yml) and then the release callee workflow (.github/workflows/release-callee.yml)

Example Runs

This is an example build workflow run triggered by a PR.

This is an example release workflow run triggered by a new release

• Note: this run has a failure due to lack of gh-pages on my fork, etc.

[lorennorman]

Looks great, good job finding the reusable workflow stuff! 💯