Fix memory safety problem with Array.from_cpointer
Previously, the from_cpointer method in arrays would trust the user to pass a valid pointer. This created an issue where the user could pass a null pointer using Pointer.create, leading to a situation where memory safety could be violated by trying to access an element of the array. This change makes it safe to pass a null pointer to from_cpointer, which will create a zero-length array.
Fix bad package names in generated documentation
Previously when you used ponyc's documentation generation functions on a code base that used relative imports like use "../foo", the package name in the generated documentation would be incorrect.