Minimap2-2.12 (r827)

Changes to minimap2:

• Added option --split-prefix to write proper alignments (correct mapping
  quality and clustered query sequences) given a multi-part index (#141 and
  #189; mostly by @hasindu2008).

• Fixed a memory leak when option -y is in use.

Changes to mappy:

• Support the MD/cs tag (#183 and #203).

• Allow mappy to index a single sequence, to add extra flags and to change the
  scoring system.

Minimap2 should produce alignments identical to v2.11.

(2.12: 6 August 2018, r827)