Allow peripherals to have multiple types (#963)

Peripherals can now have multiple types:
 - A single primary type. This is the same as the current idea of a
   type - some identifier which (mostly) uniquely identifies this kind
   of peripheral. For instance, "speaker" or "minecraft:chest".

 - 0 or more "additional" types. These are more like traits, and
   describe what other behaviour the peripheral has - is it an
   inventory? Does it supply additional peripherals (like a wired
   modem)?.

This is mostly intended for the generic peripheral system, but it might
prove useful elsewhere too - we'll have to see!

 - peripheral.getType (and modem.getTypeRemote) now returns 1 or more
   values, rather than exactly one.
 - Add a new peripheral.hasType (and modem.hasTypeRemote) function which
   determines if a peripheral has the given type (primary or
   additional).
 - Change peripheral.find and all internal peripheral methods to use
   peripheral.hasType instead.
 - Update the peripherals program to show all types

This effectively allows you to do things like
`peripheral.find("inventory")` to find all inventories.

This also rewrites the introduction to the peripheral API, hopefully
making it a little more useful.

doc/events/redstone.md

@@ -2,7 +2,7 @@
 module: [kind=event] redstone
 ---
 
-The @{redstone} event is fired whenever any redstone inputs on the computer change.
+The @{event!redstone} event is fired whenever any redstone inputs on the computer change.
 
 ## Example
 Prints a message when a redstone input changes: