python: add VERSION file

python: add VERSION file

Python infrastructure as it exists today is not capable reliably of
single-sourcing a package version from a parent directory. The authors
of pip are working to correct this, but as of today this is not possible.

The problem is that when using pip to build and install a python
package, it copies files over to a temporary directory and performs its
build there. This loses access to any information in the parent
directory, including git itself.

Further, Python versions have a standard (PEP 440) that may or may not
follow QEMU's versioning. In general, it does; but naturally QEMU does
not follow PEP 440. To avoid any automatically-generated conflict, a
manual version file is preferred.

I am proposing:

- Python tooling follows the QEMU version, indirectly, but with a major
  version of 0 to indicate that the API is not expected to be
  stable. This would mean version 0.5.2.0, 0.5.1.1, 0.5.3.0, etc.

- In the event that a Python package needs to be updated independently
  of the QEMU version, a pre-release alpha version should be preferred,
  but *only* after inclusion to the qemu development or stable branches.

  e.g. 0.5.2.0a1, 0.5.2.0a2, and so on should be preferred prior to
  5.2.0's release.

- The Python core tooling makes absolutely no version compatibility
  checks or constraints. It *may* work with releases of QEMU from the
  past or future, but it is not required to.

  i.e., "qemu.machine" will, for now, remain in lock-step with QEMU.

- We reserve the right to split the qemu package into independently
  versioned subpackages at a later date. This might allow for us to
  begin versioning QMP independently from QEMU at a later date, if
  we so choose.

Implement this versioning scheme by adding a VERSION file and setting it
to 0.6.0.0a1.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Cleber Rosa <crosa@redhat.com>
Message-id: 20210527211715.394144-12-jsnow@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>