Generated build files from zookeeper-client-c should be in target/ directory

Currently, the zookeeper-client/zookeeper-client-c generates a bunch of automake files directly in the source tree.

Placing intermediate build files directly in the source tree can cause problems, such as accidentally checking them in to the source tree using the project's SCM (git). These files are currently in .gitignore, so that issue is somewhat mitigated, but they can still be added accidentally, even if they are ignored.

The bigger problem is that Maven plugins assume that most everything that is not in a target/ directory is a source file. This can cause the apache-rat-plugin's check to fail except on a clean checkout, and can cause the maven-assembly-plugin to include those files in assemblies it creates, among other problems.

These files should be generated in the target/ directory during the build, and removed from .gitignore. If they are needed in an assembly, they should be explicitly added with the appropriate assembly descriptor during the build.

I would work on this, but I'm not adequately familiar with the C parts of the build. If somebody works on this, I'd be happy to help review or consult, as needed to fix this.