Document and greatly improve TSP algorithms (#386)

- Add LEMON headers.
- Add Doxygen doc for all classes and their members.
- Clarify and unify the public API of the algorithms.
- Various small improvements in the implementations to make
them clearer and faster.
- Avoid using adaptors in ChristofidesTsp.

EXTRA_DIST += \

	scripts/bib2dox.py \

	scripts/bootstrap.sh \

	scripts/chg-len.py \

	scripts/mk-release.sh \

	scripts/unify-sources.sh \

	scripts/valgrind-wrapper.sh