Consume instance from stdin.

This commit is a small change in the way we get the list of instances to run.
Before this commit, we are supposed to give an SNR, a K and an instance range.
It therefore assumes that a given instance has an SNR, and a K.
More precisely, the instance format MUST follow:
SA_SNRxx_Kyy_instancezz
Where xx, yy and zz are integers.
This format is absolutely arbitrary, and comes from the first dataset
used to test the code.
After this commit, the arguments SNR, K, instance are removed.
Instead, we get a list of instances, one instance per line, from stdin.