Restructure stats for re-use

[ibboard]

The current stats require duplication, but a lot of stats (e.g. "a goblin) are common. It would be more efficient if we could reference these central stats. It would also make extensions that care about trooper type more than unit type (i.e. "goblin" rather than "goblin spearman") a bit easier.

Included in this restructure we should allow per-unit stats with no requirement to reference and re-use (i.e. the current behaviour), per-unit overrides with references (i.e. a reference and a current behaviour) and multiple stat lines.

[ibboard]

(In r548) Re #268: Restructure stats for re-use

• Add "Member Type" class
• Add member type setting and getting to Race
• Load member types from XML files
• Make unit type pull stat line from stats or first member type, or fall back to a blank stat line
• Change Stats object to initialise blank values
• Change schema
  • Make stats optional
  • Add member type list to race
  • Add optional member type references to units

[ibboard]

(In r549) Re #268: Restructure stats for re-use

• Test new stat line behaviour

[ibboard]

(In r550) Re #268: Restructure stats for re-use

• Add multi-stat properties to unit types
• Deprecate single versions and make them return just the first stat line (since we guarantee at least one line)

[ibboard]

(In r551) Re #268: Restructure stats for re-use

• Add tests for multiple stat lines/referenced types and for overriding the stats

[ibboard]

(In r552) Fixes #268: Restructure stats for re-use

• Present new stats through Unit
• Add property to get array of type IDs

[ibboard]

Release as part of v0.1b9