Add support for Doxygen-based documentation.
Makefile: add doc and clean-doc targets.
Doxyfile: new, configuration for Doxygen.
Add various tags and adjustments throughout for Doxygen use.

Object.hh: fully document unit.
Object.cc: reorder to match member groupings in documentation.

README: remove most text, now found on main page of documentation.
Thief.hh: add main page text from README, with revisions.