Initial proof-of-concept for partial ship costs

 This is an initial implementation of issue #33. There are a number
 of known problems thus far:

 * Crew absent from a ship (Orz marines for instance) are not
   counted for scoring purposes currently
 * Only the modified value is shown
 * This code may cause release builds to segfault as currently
   written.
Absent CREW_OBJECTs should now be counted

 calculate_crew_percentage now accepts a second
 parameter, which contains a delta to be applied
 to the ship's crew level before percentage
 calculation. This is used currently to account
 for CREW_OBJECTs (Syreen Song crew, Ur-Quan
 fighters, etc) which should be counted as crew
 for the purposes of scoring. Currently, active
 Syreen Song crew are always included for the
 purposes of scoring, as well as any Ur-Quan
 fighters or Orz marines that belong to the
 ship being evaluated.
minor cleanup in element.h
Merge branch 'master' of github.com:Roisack/Shiver-Balance-Mod into partial_cost
Adjusted values now are displayed better

 The adjusted score is now displayed as a decimal (e.g.
 12.7), in parentheses. GetRaceQueueValue now takes a
 second parameter and returns double to facilitate this.
Account for 42-crew Syreen correctly
Properly account for retreated ships
rm stray debug print
Fix bug: unspawned Syreen are now counted properly
Merge branch 'partial_cost'