rough implementation of newskald spells

new spells: infusion, song of slaying, spectral weapon, spirit shield
new book: book of battle
new mons: MONS_SPECTRAL_WEAPON
slightly improved behavior for spectral weapon

the weapon will now approach attacked monsters in more situations, but still a weird problem exists where it gets "stuck" behind you occasionally...
increase hp of spectral weapons
fixed movement for spectral weapons

it now correctly approaches monsters you attack, returning to your side when you retreat or the monster is dead
add every-turn noise when you are under sos effect
basic descriptions for newskald spells and spectral weapon monster
reduce base damage of spectral weapons to 1
add a "stop singing" ability for sos users
make spectral weapon boring!
make spectral weapons disappear when you unwield
adjust infusion slightly

removed the 0 mp 1 dmg bonus and fixed its normal bonus to 3
adjust what kills increase the song of slaying's bonus
remove the +1 enchantment from skald starting weapon
Merge remote-tracking branch 'origin' into newskalds
buff plain spectral weapon

allow the player's skill bonus to add slaying to the spectral weapon's weapon, increase base damage and hp of the spectral weapon monster
add pow/25 boost to infusion damage
adjust comments slightly
Merge branch 'master' into newskalds
update class-pick description of skalds
Merge branch 'master' into newskalds