Egor ask-and-tell interface

[relf]

This PR refactors the Egor API to make a proper ask-and-tell interface with Python binding. It involves some breaking changes in the API

• Configuration of Egor is factorize out in EgorConfig
• EgorBuilder gets a configure method to tune the configuration
• EgorService structure represent Egor when used as service
• Python Egor API changes:
  • function under optimization is now given via minimize(fun, max_iters=...) method
  • new method suggest(xdoe, ydoe) allows to ask for x suggestion and tell current function evaluations
  • new method get_result(xdoe, ydoe) to get the best evaluation (ie minimum) from given ones