Make Promise.Bool a multi

otherwise "so Promise" dies
a tiny speedup for auto-generated attribute accessors
Make .end a multi
Make .Int a multi
Add types to signature and make multi

Fix several cases where Type.method would give a "cannot access attribute in
a type object": should that happen now, it should give you a "cannot find
candidate", or should just work.
Update synopsis link to design.perl6.org
Merge branch 'nom' into newio