Editing EDF item effects and inventory

Define what happens when an item is picked up (and eventually, used or dropped from the inventory - this is not complete yet).

There are many different types of item effect definitions:
===artifact===
An artifact is an item which, when collected, goes into the player's inventory.

 artifact <name>
 {
  amount         <int> // amount gained with one pickup
  maxamount      <int> // max amount that can be carried in inventory
  interhubamount <int> // max amount carryable between levels in different hubs;
                       // -1 if this field should not apply at all
  sortorder      <int> // key used for sorting the player's inventory
  icon           <str> // name of icon graphic for invbar (currently unused)
  usesound       <str> // sound made when item is used (currently unused)
  useeffect      <str> // name of item effect to use for activation (unused)
  
  [+-]undroppable      // if +, cannot be dropped from inventory
  [+-]invbar           // if +, appears in invbar; otherwise, invisible
  [+-]keepdepleted     // if +, will remain in inventory with amount of zero
  [+-]fullamountonly   // if +, cannot pickup unless full amount is needed
  
  // artifacttype determines what sort of artifact this is.  
  artifacttype   <str> // "Normal", "Ammo", "Key", "Puzzle", "Power", "Weapon",
                       // or "Quest"
                       
  // The following fields apply only to certain artifact types. They have no
  // effect if specified on other types.
  
  // Ammo
  ammo.backpackamount    <int> // amount of this ammo type given by a Backpack
  ammo.backpackmaxamount <int> // max amount after collecting a Backpack
 }
===healtheffect===
A health effect gives the player health in one of many possible ways. 
 healtheffect <name>
 {
  amount     <int> // amount of health to give
  maxamount  <int> // max amount this item can health to; if player has greater
                   // health, the item cannot be picked up at all.
  lowmessage <str> // alternate message to give instead of pickupfx message when
                   // health is < amount; if starts with $, is a BEX mnemonic.
  
  [+-]alwayspickup  // if +, item is picked up even when unneeded (ie Health Bonus)
  [+-]sethealth     // if +, item SETS health rather than adding to it (ie Megasphere)
 }
===armoreffect===
An armor effect defines the properties of player armor 
 armoreffect <name>
 {
  saveamount    <int> // amount of armor given
  savefactor    <int> // numerator of fraction determining save percentage
  savedivisor   <int> // denominator of fraction determining save percentage
  maxsaveamount <int> // max amount his item can give; if player has greater
                      // armor, the item cannot be picked up at all
                      
  [+-]alwayspickup    // item is picked up even when unneeded (ie Armor Bonus)
  [+-]bonus           // if +, is a bonus (adds to current armor type without
                      // changing the protective qualities)
 }
===ammoeffect===
Ammo givers give an Ammo type artifact to the player.
 ammoeffect <name>
 {
  ammo       <str> // Name of an Ammo-type artifact definition
  amount     <int> // Amount to give for an ordinary pickup
  dropamount <int> // Amount to give if dropped by an enemy
  
  [+-]ignoreskill  // if +, does not double on skills that give double ammo  
 }