Fix inconsistencies in method/struct naming

[petehayes102]

Cases that I'm currently aware of:

• File::mv vs. File::copy - should also have File::cp and File::move with the long names as aliases
• DirectoryOpts vs FileOptions - Should be DirectoryOptions, deprecate DirectoryOpts
• Service::new_service() accepts a ServiceRunnable::Service OR ServiceRunnable::Command, which is misleading. Should perhaps be Service::new_runnable?