Megfile

- `megfile.s3` retries when server returns 500 - 503
- remove `megfile.lib.fakefs`

- `megfile.s3.s3_memory_open` support ab / rb+ / wb+ / ab+ mode
- `megfile.s3.s3_open` support ab / rb+ / wb+ / ab+ mode (by using s3_memory_open)
- Speed up `s3_glob`
- Accept `s3.endpoint_url` in aws config file

- __[Breaking]__ Rename `megfile.interfaces.MegfilePathLike` to `megfile.interfaces.PathLike`
- Fix ungloblize

- __[Breaking]__ Rename `megfile.s3.MEGFILE_MD5_HEADER` to `megfile.s3.content_md5_header`
- __[Breaking]__ Remove `megfile.lib.get_image_size`, `megfile.smart.smart_load_image_metadata` and `megfile.smart.IMAGE_EXTNAMES`

- Refactor `process_local` / `thread_local`, remove dependency on `multiprocessing.utils.register_after_fork`

- Speed up `s3_glob`