Demux

This should do the trick:
```python
from re import search
result = search('^(?P<sample>.+?)_\d+? .*orig_bc=(?P<orig_bc>.+?) new_bc=(?P<corr_bc>.+?) bc_diffs=(?P<bc_diffs>\d+)', rec['SequenceID'])
if result is not None:
    raise ValueError("%s doesn't appear to be split libraries "
                     "output!" % fp)
sample = result.group('sample')
bc_diffs = result.group('bc_diffs')
corr_bc = result.group('corr_bc')
orig_bc = result.group('orig_bc')
```
Of course, the regex could be simplified some, but then we wouldn't get the neat way to reference the groups by name!