Restructure strategies folder about axelrod

[drvinceknight]

Have created 5.0.0 (we can easily change the name).

[alexhroom]

on the part of the discussion regarding importing 'generic' strategies into specific game namespaces:
I've managed to write a way of conditionally importing classes from a shared 'generic' library file based on features of said classes. A minimal working example is here!

e.g. with this, it's possible for the initialisation of, say, axelrod.strategies.ipd to get the set of generic strategies and import the ones with strategy.assumptions_satisfy(ipd_characteristics) in the axelrod.strategies.ipd namespace with whatever modifications; so axelrod.strategies.generic.TitForTat would tit for tat between {0, 1} whereas axelrod.strategies.ipd.TitForTat would 'borrow' the generic strategy but modify it to produce {C, D}!

[alexhroom]

As a side note, if we are working towards breaking changes like this, @drvinceknight I recommend the repo adds a 5.0.0_dev branch to push 5.0.0 changes to so that PRs etc. towards 5.0.0 can be made

[drvinceknight]

I recommend the repo adds a 5.0.0_dev branch to push 5.0.0 changes to so that PRs etc. towards 5.0.0 can be made

Good idea. Could just call it 5.0.0 which would serve the same purpose (don't actually care what we call it).