0.4.0: Improved USM memory manager

• New device info attributes are exposed using SyclDevice
  • max_compute_units
  • max_work_item_dimensions
  • max_work_item_sizes
  • max_work_group_size
  • max_num_sub_groups
  • aspects for int64 atomics
• Major changes and improvements to dpctl.memory
  • MemoryUSM* classes moved to dpctl.memory module,
  • added support for aligned allocation, added support for prefetch and mem_advise (sychronous) methods, implemented copy_to_host, copy_from_host and copy_from_device methods, pickling support, and zero-copy interoperability with Python objects which implement sycl_usm_array_inerface protocol.
• Helper scripts to generate API documentation for both C API and Python.
• Other improvements and bug fixes.