add cfg for hex values if we want upper or lowercase letters

[Richie94]

For issue #717 I tried to make this configurable.

Its my first PR here, I didnt found a good spot for testing, would be nice if you can point me out where to do this.

[cowtowncoder]

Looks mostly good, thank you for contributing this!

As to testing, I think it should go somewhere under com.fasterxml.jackson.core.write, perhaps GeneratorBasicTest, or new test class. Should cover all implementations.

Aside from that, one thing I will need before merging (and about only thing) is CLA.
It can be found here:

https://github.com/FasterXML/jackson/blob/master/contributor-agreement.pdf

(or Corporate CCLA next to it).

the usual way is to print, fill & sign, scan, email to info at fasterxml dot com.
With that I can merge this and it can still make it in 2.14.0 release (or -rc2 first maybe).

Looking forward to merging this!

[Richie94]

Thx for fast feedback, ill print the CLA out tomorrow and send it to you.

[Richie94]

Okay, Mail should be in your inbox.

[cowtowncoder]

CLA received, can merge.