Add cabe-maven-plugin

[mk868]

This is a initial implementation of the maven plugin - there's still plenty of room for improvement, but the basic assumptions work.

During the implementation, I encountered an issue: the class files produced by the maven-compiler-plugin are placed in the target/classes directory, but they are not regenerated when the source files remain unchanged.
This caused the cabe-maven-plugin to repeatedly perform instrumentation on the same class files.
To address this, in the example project, I redirected the compilation results to a temporary directory, target/unprocessed-classes.
This guarantees that the instrumentation is performed only once.
I discovered this approach in AspectJ Maven Plugin.

Changes in this PR:

• the cabe-maven-plugin project added
• the examples/hello-maven project added
• Fixed typo in the usage description

Related: #13

[xzel23]

Thank you, I will have a look in the coming days.