Future lingen

future-lingen is a rather long-lived branch. Its original goal is to include recent (spring-fall 2019) developments that make it possible for lingen to auto-tune the thresholds for the various algorithms it can use, and do as well much better multithreading. Code from this branch was used for both rsa240 and dlp240 records.

The only reason why it's not merged at the moment is that the very feature mentioned above sometimes has a hard time measuring the time of the elementary operations that are used in lingen. This results in suboptimal thresholds. To make best use of the code, the "timing schedule" must be adjusted more or less by hand, which is a pity.