argument parser improvements

[jpdown]

• [ ] string
• [ ] int
• [ ] number
• [ ] bool
• [ ] user
• [ ] channel
• [ ] guild channel
• [ ] role
• [ ] timestamp
• [ ] emote (https://stackoverflow.com/a/69220565)

[jpdown]

timestamp parsing for #24

[jpdown]

https://github.com/Microsoft/TypeScript/issues/26019#issuecomment-408547279 this could help

[jpdown]

allow parsing user with username#discriminator

[jpdown]

use these built in patterns https://discord.js.org/#/docs/main/stable/class/MessageMentions?scrollTo=s-CHANNELS_PATTERN