fast mode

this release adds a --fast-mode flag that makes mosdepth almost twice as fast. It does not look at mate overlap and it doesn't look at insertion or deletion events in the cigar -- it will still show large deletions with coverage changes and it still skips soft clipped portions of reads. This behavior is likely desirable in many cases and will result in an additional 2X speedup.

0.2.4

• Add optional --include-flag to allow counting only reads that have some bits in the specified flag set.
  This will only be used rarely--e.g. to count only supplemental reads, use -F 0 --include-flag 2048.
• Fix case when only a single argument was given to --quantize
• add --read-groups option to allow specifying that only certain read-groups should be used in the depth calculation. (#60)
• add --fast-mode that does not look at internal cigar operations like (I)insertions or (D)eletions, but does consider soft and
  hard-clips at the end of the alignment. Also does not correct for mate overlap. This makes mosdepth as much as 2X faster for
  CRAM and is likely the desired mode for people using the depth for CNV or general coverage values as drops in coverage
  due to CIGAR operations are often not of interest for coverage-based analyses.