palette protocol

[itepastra]

Adds a feature for a palette based protocol,
where a random 256 color palette is generated and clients can only use those to write to the canvas

closes #6

• add Clone and to_bytes() to Color as utilities
• add the palette protocol, with up to 256 colors in the palette
• feature flags for use statements
• make the writes and flush await
• initialize with random palette
• rename constant to be more descriptive
• add test for parsing palette set command