Merge fuzzer and generator implementations and regroup by types being supported rather than by technical level.

[jcornaz]

Example of how it can be organized:

• Int
  • Generator
  • Simplifier
  • Fuzzer
• String
  • Generator
  • Simplifier
  • Fuzzer

The rational is that a triplet Generator/Simplifier/Fuzzer is more cohesive than 2 arbitrary supported types (Like Int with String)