v1.9.0

Added

• Changelog
• Static executable statically-linked against glibc/libgcc/libstd++ [#101,#163]
• Script to build the gramtools backend (build.sh). Simplifies CI (docker image building), removes
  hacking into setup.py, and simplifies compiling on user machine.

Changed

• Switched from setup.py to pyproject.toml and setup.cfg [#164], following PEP517

Removed

• Retired variant-aware kmer indexing code [#159]
• No longer install py-cortex-api by default. If gramtools discover is used,
  its installation is requested

Fixed

• Variant rebasing in discover was incompletely tested- simplified algorithm and added tests
• Infinite loop when no reads mapped to genome graph