Link.hh: fully document unit.

Flavor: make ANY a Flavor; make Number ctor explicit; check for validity in name ctors.

Link: reimplement get_one without GetSingleLink to avoid assertion; remove String overloads of data field internals, converting in template methods instead.
Link::Inheritance: rename DEST to DESTINATION.
Link::List: new typedef replacing namespace-level "Links".

THIEF_LINK_FLAVOR: combined macro replacing THIEF_FLAVORED_LINK and THIEF_FLAVORED_LINK_COMMON; new List typedef replacing namespace-level version.
LINK_FLAVOR_IMPL: collapse to one form only, renamed from FLAVORED_LINK_IMPL; don't check validity in NONE and copy ctors.
(link flavor classes): check for existence of link before setting data fields in create methods.
FlinderizeLink: put defaults on impulse and scatter args to create method.
PhysAttachLink: put default on offset arg to create method.

Message: add is_postable method to prevent posts of custom message structures.
LinkMessage, PropertyMessage, ConversationMessage: add is_postable returning false.
LinkMessage: rename Event::ADD to CREATE and Event::REMOVE to DESTROY; rename "LinkAdd" to "LinkCreate" and "LinkRemove" to "LinkDestroy"; move to Message unit to allow inclusion of Link unit there.
OSL: don't issue link messages for unrecognized events.

MissingResource: new exception; use throughout.

Object::List: new typedef replacing namespace-level "Objects".
AI::List: new typedef replacing namespace-level "AIs".

Makefile: add INLINES list and have doc target depend on it.
Doxyfile: add another predefined macro that isn't always expanding.
(various): standardize syntax of brief class descriptions.