Stefan Walter

Optionally use external spdlog library

3

As mentioned in #7, it would be nice to allow external dependencies to be used. This helps e.g. if you already have spdlog as a dependency in your CMake build....

According to the [discussion](https://discuss.gradle.org/t/how-to-declare-a-dependency-on-another-configurations-artifact-in-the-same-project/8814) in the Gradle forum, `@InputFiles` would be the correct annotation to implicitly register a task's dependencies. With `@Input`, I still have to explicitly register dependencies so...