Add getVersion()

[nseidle]

This PR:

• Adds a helper to return the obtained version string from the JSON file.
• Adds to the further example demo'ing how to use getVersion().

I needed this so that I could check the version and show it to the user before they agreed to proceed with update.

It's an open question if other variables need to be exposed.

Love the library. Thanks for this!

[mikalhart]

Many thanks for this...!

[mikalhart]

@nseidle I decided to change new method to GetVersion() (with capital G) just to maintain consistency with other methods. (Hope this doesn't cause too much heartache?) But thanks again. This is an obvious and useful addition that I should have thought of...!