some change output format
Enhanced #inspect output
Add Fixnum#to_color
Add #succ alias of #next
Change behaviour when adding(subtruct) over the range
RGB#+, #- can take RGB object
Color#+, #- can take Color object
Fix RGB#+ #- with RGB object
Fix test
Add #*, #/
Fix #+, #-
refactoring
Update comments on methods
Add #+, #-, #*, #/ for color object composition
Update method comments