Add min_bler as stopping condition in sim_ber

[nbecker]

I have some long-running simulations and one thing that I think would be helpful is to add to sim_ber an option to stop if the BLER obtained on the last esno point is below some threshold. For example, I am only plotting results down to 1e-5. If the last esno point is below 1e-5 I'd like to stop rather than continuing until there are 0 block errors, to save time.

[faycalaa]

Hi,

We plan to add this feature in the next release.

[SebastianCa]

Please see #257 for further discussion.