Updates to deal with ASU contents for multiple crystals (including sequence data): 1. Crystal class: added methods to set and retrieve the sequence data. 2. Xia2run class: sequences are now assigned to crystals. 3. New module-level function "splitlines" (breaks text into lines of    fixed length). 4. __main__: pattern for capturing sequence from xia2.txt updated to    deal with "blank" sequences. 5. __main__: reporting in "Asymmetric unit" sections modified for    multiple crystals, and now also include the sequence.
Updates to deal with ASU contents for multiple crystals (including
sequence data):
1. Crystal class: added methods to set and retrieve the sequence data.
2. Xia2run class: sequences are now assigned to crystals.
3. New module-level function "splitlines" (breaks text into lines of
   fixed length).
4. __main__: pattern for capturing sequence from xia2.txt updated to
   deal with "blank" sequences.
5. __main__: reporting in "Asymmetric unit" sections modified for
   multiple crystals, and now also include the sequence.

xia2/xia2,xia2/xia2