get python versions from 32&64-bit registry views

[Tithen-Firion]

On Windows, get Python paths from both 32-bit and 64-bit registry views.

Additionally you get both major and minor versions, both with and without bitness information.

For example if you have versions 3.5 (32 bit), 3.5 (64 bit) and 3.6 (32 bit) you can choose from: 3.5-32, 3.5-64, 3.6-32, 3.5, 3.6, 3-32, 3-64 and 3, where:

• 3 == 3.6-32 (because it has the highest version)
• 3-32 == 3.6-32
• 3-64 == 3.5-64
• 3.5 == 3.5-64 (because 64-bit wins over 32-bit)
• 3.6 == 3.6-32

[gaborbernat]

let's add a changelog detailing the effect on users in detail 👌