Start coloring on given POSet

Property definitions

nitc $ POSetColorer :: colorize
	# Start coloring on given POSet
	fun colorize(poset: POSet[E]) do
		poset_cache = poset
		graph = new POSetConflictGraph[E](poset)
		allocate_ids
		compute_colors
		conflicts_cache = graph.conflicts
		is_colored = true
	end
src/compiler/coloring.nit:215,2--223,4