0.12.2

Fixed

• the install script did nothing on macOS. It tested uname against the lowercase darwin,
  where uname answers Darwin, so the branch that installs the binary never ran and the
  script exited reporting success. Only the Linux branch had ever worked

• the install script unpacked the archive into whatever directory it was run from and removed
  only the tarball afterwards, leaving the binary behind there. It works in a temporary
  directory that is removed however it exits

Added

• the install script verifies the archive against the checksums.txt published beside it, and
  refuses to install a download that does not match. It also reads IPSCOUT_VERSION to pin a
  release, IPSCOUT_INSTALL_DIR to install somewhere other than /usr/local/bin, and
  GITHUB_URL for a mirror. It creates the install directory if it is missing, reaches for
  sudo only when the directory cannot be written to otherwise, and says so when the directory
  is not on your PATH