v2.5.0

• Overall improvements in the use of prefetch instructions. (contribution by Igor Sfiligoi)
• Made input/output fully asynchronous by using a dedicated thread. (contribution by Igor Sfiligoi)
• Added support for AVX2 256-bit instructions with can be enabled by
  setting the SSE_AXV2 environment variable at compile time. (contribution by Igor Sfiligoi)
• Fixed an issue causing bowtie2 to crash when processing ZSTD
  files with high compression ratios.
• Changed the way that unique alignments are counted in summary
  message to better match up with filters on SAM output