Support arbitrary `<String, ?>` maps.

[zenfyrdev]

Currently, Commander does not allow any arbitrary maps. It's impossible to know what type the map is without holding on to the field/method return type info.

Since, ReflectiveMapStructure already has the type info, it may be possible to figure out the type and supply converters accordingly.

• Type parsing
  • Fields
  • Methods
• Map types
  • Base Map interface.
  • Common Map subclasses. Like Immutable and Identity maps.
  • Enum Maps
• Support multiple string-like key types. Like Identifiers.