Merge pull request #3 from chrishd/master

Strategien sind jetzt Klassen
-sl argument added

-sl argument allows to specify a list of strategies to be included in
the tournament. If unspecified, all available enter.
- fixed plotall bug (folder creation - thx chrishd)
- added titfortwotat strategy
runs a tournament for every possible strategy combination

- make sure to use the -sl parameter to specify a list of strategies to
consider, otherwise it might take ages.
- to do: instead of outputting to the command line, generate a human
readable summary file
modified Prisoners' Dilemma - higher payoffs are better.

also changed Leaderbord to work correctly without reversal

New payoffs are:
a = 2, b = 0, c = 3, d = 1.
These fulfil both requirements:
1) c > a > d > b  (wiki: T>R>P>S)
2) 2*a > c + b  (wiki: 2*R > T+S)
solving merge conflict
neuster Stand. +testing.py +run-all-combos.py