EpsilonPolicy now has a common interface: EpsilonPolicyInterface.

Before EpsilonPolicy was implemented solely in terms of discrete
states. Now it is an interface that can be used both with
discrete states that with Beliefs.
The old EpsilonPolicy is now simply an instantiation of the templated
class EpsilonPolicyInterface. It was also moved inside the MDP
namespace, as all other MDP policies are.
Fixes QGreedyPolicy.cpp. May have to fix elsewhere.
Fix simplification.
Merge pull request #8 from EHadoux/hotfix/QGreedyPolicy

Fixes QGreedyPolicy.cpp. May have to fix elsewhere.
New functions to test equality/difference with probability values and
appropriate fixes.
Inlined functions to prevent redefinitions in linking