skip short seqs

[siebrenf]

C function pfmscan() will now stop if the given sequence is shorter than the given pfm.

I'm not sure if this does anything other than stopping early, because the line if (j_max < 0) { j_max = 0;}, in line 739 (743 in this PR), should already take care of problems?

How to test:

Command line:

git clone [email protected]:vanheeringen-lab/gimmemotifs.git
cd gimmemotifs
git checkout option_2
python setup.py build && pip install .

Python:

from gimmemotifs.c_metrics import pfmscan

seq = "ATGGTCT"
# ppm and cutoff for 'MA0046.2_MA0046.2.HNF1A'
ppm = [[0.3681, 0.1725, 0.2467, 0.2127],
       [0.4593, 0.0273, 0.4716, 0.0418],
       [0.0228, 0.0643, 0.0548, 0.8581],
       [0.1474, 0.1097, 0.0275, 0.7154],
       [0.9817, 0.0002, 0.0171, 0.001],
       [0.9337, 0.0418, 0.0005, 0.024],
       [0.0804, 0.0267, 0.0004, 0.8925],
       [0.2361, 0.265, 0.3209, 0.178],
       [0.934, 0.0006, 0.0224, 0.043],
       [0.0452, 0.0008, 0.0538, 0.9002],
       [0.0029, 0.0158, 0.0003, 0.981],
       [0.815, 0.0137, 0.077, 0.0943],
       [0.8781, 0.0431, 0.068, 0.0108],
       [0.0865, 0.8223, 0.0381, 0.0531],
       [0.2807, 0.2422, 0.1608, 0.3163]]
c = 9.687735324685306
nreport = 50
scan_rc = True

result = pfmscan(seq.upper(), ppm, c, nreport, scan_rc)
print(result)