v1.5.0: Initial Support for Permissions v2

Changes

• Initial support for Permissions V2's default_member_permissions field (#81, thanks @therealr5!) - related to discord/discord-api-docs#4830
• Hotfix for the disabled bulk permissions endpoint
• Updated Option model to support subcommands, min/max value, channel type (#84, thanks @therealr5!)

Here be dragons

Permissions overwrites don't seem to be functioning properly after the permissions V2 rollout, track #85 for updates. Code using default_permission or ctx.overwrite_permissions() will likely fail. The new default_member_permissions field is unaffected.