support for .alternatives file

Note that the v3.0 was never released but existed only on the master branch. But since the release was marked in the commit, a new version is being released instead of reusing the same version

v3.1 changelog

Changes in this release:

• use TERMUX_SCRIPTDIR instead of TERMUX_PKG_CACHEDIR
  Commit Id: df8d622

v3.0 changelog

For the full list of changes, kindly look at the commit history. This
only lists changes that are major.

Major Changes:

• use javascript Map instead of Object
  Commit Id: f79de15

• add support for '.alternatives' file (Debian Alternatives)
  Commit Id: 1f8268b

• Bump CMake version requirement >= 3.25
  Commit Id: 0d590a1

Minor Changes:

• only download Contents.gz file for the architecture we are building
  for
  Commit Id: 5faf3d0

Full Changelog: 2.4.0...3.1