Ensure the --version output is easy to parse

[pombredanne]

Today's output of the --version option requires some work to be parsed:

$ ./scancode --version
ScanCode version 30.1.0
ScanCode Output Format version 2.0.0
SPDX License list version 3.15

we should instead make it valid YAML such that this is easy to read for human and parse for tools:

$ ./scancode --version
ScanCode version: 30.1.0
ScanCode Output Format version: 2.0.0
SPDX License list version: 3.15

This would be enough!

$ python
>>> import saneyaml
>>> a='''ScanCode version: 30.1.0
... ScanCode Output Format version: 2.0.0
... SPDX License list version: 3.15
... '''
>>> saneyaml.load(a)
{'ScanCode version': '30.1.0', 'ScanCode Output Format version': '2.0.0', 'SPDX License list version': '3.15'}