Add a set of new CLI commands, called `mle memory` which provides memory CRUD

[huangyz0918]

Add a set of new CLI commands, called mle memory which provides memory CRUD.

• mle memory --add <file/or dir>
• mle memory --rm <file_key>: right now the file key is the absolute file path when saving, can the code will be divided into several chunks, --rm should remove all chunks with the same file name.
• mle memory --update <file_key>: just remove all related chunks and add the file again

Originally posted by @huangyz0918 in #269 (comment)