Assorted cleanup

[mikowitz]

• Consolidate docs using Xairo.point() type
• Add Point.from/1 and Point.from/2
  • The ablity to wrap this around both Point structs and tuple pairs allows a lot of deduplication around converting tuples to points
• Split Rust code into smaller modules
• Fill in guards for new functions
• Add mix dialyzer
• Update Inspect implementations
• Update README