Megfile

- fix
- fix tqdm unit divisor to `1024`
- feat
- all open func support `encoding` and `errors` parameters
- add `HttpPrefetchReader` for perf http open

- fix
- change retry log leval to info
- fix `megfile head` command error from http path
- fix retry not work in prefetch_reader
- fix upload and download when local file path with protocol, like `file:///data/test.txt`

- breaking change
- sftp path protocol change for supporting relative path
- new protocol:
‒ sftp://[username[:password]]hostname[:port]//absolute_file_path
‒ sftp://[username[:password]]hostname[:port]/relative_file_path
- feat
- cli
- Add `megfile to` command, can write content from stdin to a file
- Add `megfile head` and `megfile tail` command
- Add http and stdio methods in `__init__.py`, now you can from megfile import them

- feat
- add `SmartCache`, and `smart_cache` support more protocol

- fix
- fix the cleanup behavior of ThreadLocal after forking

- feat
- add `http_exists`