ENH: CONESTA use curent mu as stoping criterium intsead of function.mu_opt(self.eps).
- Some refactorization of the algo: simplify variables names and suffix optional returned
information variable with "_" to  spot optional variables ex: mu_, t_, f_ are.
- Avoid unnecessary computation of the gap within CONESTA get it from the last FISTA
iteration.
Same modification for StaticCONESTA
Merge pull request #2 from duchesnay/master

ENH: Changes to CONESTA's stopping criterion and other minor changes.