Add XY chart

[timqian]

Improve code while adding this new chart so other people can contribute easier

• [x] yLabel better position
• [x] configurable charts via options
  • [x] config tick number
  • [x] config legend position
  • [x] config with/height?
  • [ ] ... to be added
• [x] ~smart margin(according to ylabel length)~ 1000 => 1k if number too large
• [x] extract reusabel functions (part of it: add axis; add labesl;)
• [x] improve doc
• [x] doc for the code structure and how to add new graph