add encodings of csplib problems

[jwaldmann]

CSPLIB ( http://www.csplib.org/ ) contains combinatorial problems that are standard in the constraints community. It would be good to have at least some of them encoded in CO4, to compare encoding (does it look nice?) and performance. (I started in CO4/CSPLIB/ ) One recurring building block seems to be the alldifferent constraint (cf. Issue #44 )

[jwaldmann]

performance data for Golomb Ruler with odd-even-sort encoding of alldifferent:

size 11
#variables: 22338, #clauses: 112372, #literals: 342231
Solver finished in 4862.366 seconds (result: True)
[(nat 7 1),(nat 7 3),(nat 7 9),(nat 7 15),(nat 7 5),(nat 7 14),(nat 7 7),(nat 7 10),(nat 7 6),(nat 7 2)]

size 12
#variables: 28756, #clauses: 144846, #literals: 441448
Solver finished in 291598.532 seconds (result: True)
[(nat 7 9),(nat 7 1),(nat 7 7),(nat 7 13),(nat 7 12),(nat 7 3),(nat 7 11),(nat 7 5),(nat 7 18),(nat 7 4),(nat 7 2)]

size 12 : 80 hours = 3.5 days