Graph construction is currently subject to the circle problem

[TransGirlCodes]

The method of initial graph construction from kmers that is currently used is much more efficient now.

However, it still suffers from the circle problem in that kmers that have themselves as a de-bruijn neighbour forwards and backwards are not included in the unititgs.

This is a fairly known and simple problem to solve.

But since it's very very rare in real data, right now the algorithm just warns you. But we should fix it later.