Current LTTB (lttbc) algorithm is sometimes numerically unstable

[jvdd]

There appears to be (very minor) changes in floating point numbers when using the lttbc LTTB implementation

This causes test test_fwr_time_based_data_s to fail sometimes

A fix for this would be using our own lttb algorithm (also implemented in C) -> see #84

As for now, we will disable this test (as this only occurs in very niche use-cases) and leave this issue open until this problem is resolved (by merging #84)

[jonasvdd]

shoulde be resolved by merging #103

[jonasvdd]

Will be fixed in a new release with #103