Bracket size in tuneLearnFast()

[mfasiolo]

At the moment the function detects when the solution is close to the margins of the bracket, but it cannot be trusted 100%. It is not clear how close to the margins the brent() method can get, hence it is difficult to define a clear margin of safety (not the margin of safety is represented by aTol = 0.05).

Problems might arise if the bracket size brac gets small, so that its size is comparable to tol.