Release 1.0.5

Merged #22 (event-related) and #28 (README-related).
Added auto-register feature.
Added on_slash_command, on_slash_command_error events.
Added get_all_commands coroutine to utils.manage_commands.
Fixed type 2 and 5 not working at SlashContext.send() coroutine.
Fixed guild_ids and has_subcommands can be falsely overriden.
Changed SlashContext.guild is ID when cannot get guild from cache.
Changed some args of send and edit is keyword-only args.