peg: fix some old docs that referred to "p1".
peg: fix some old docs that referred to "p1".

nicolas-p/factor,tgunr/factor,factor/factor,bjourne/factor,slavapestov/factor,bpollack/factor,bpollack/factor,bpollack/factor,factor/factor,tgunr/factor,bjourne/factor,nicolas-p/factor,mrjbq7/factor,bpollack/factor,factor/factor,AlexIljin/factor,AlexIljin/factor,mrjbq7/factor,bjourne/factor,slavapestov/factor,slavapestov/factor,nicolas-p/factor,AlexIljin/factor,AlexIljin/factor,mrjbq7/factor,AlexIljin/factor,mrjbq7/factor,nicolas-p/factor,tgunr/factor,AlexIljin/factor,slavapestov/factor,bpollack/factor,tgunr/factor,tgunr/factor,mrjbq7/factor,nicolas-p/factor,AlexIljin/factor,nicolas-p/factor,bjourne/factor,factor/factor,bjourne/factor,mrjbq7/factor,bjourne/factor,slavapestov/factor,slavapestov/factor,bpollack/factor,nicolas-p/factor,tgunr/factor,factor/factor,bjourne/factor,slavapestov/factor,bpollack/factor,factor/factor