Add 10 new item specials affecting spawn chances

Also:
- Slimebane shoes
- Head jewellery
- A shirt which is an inverse to the cloak of shielding
- Fix magnetic ring never spawning
- As a fae you are much more likely to find enlightening potions
Use "an" instead of "a" for items beginning with a vowel
Allow two finger-slot items (ie rings) to be worn at the same time
Add new item special and new equip slot
Fix crash in lightning bolt
Add webs and tons of associated things.
- Web is implemented like poison cloud, as a "monster"
- New status effect, entangled, to enforce the web's power
- New spell, web, along with associated scroll
- New potion, silken; drink for minor nourishing, throw for web
- New passive ability, web passage, granted to spiders or to the player
- New monster, spider spinster, which throws webs

Also:
- Poison clouds now have disease immunity