Add an ISO3166 special case for Kosovo

[sam-w]

Q	A
Documentation	no
Bugfix	yes
BC Break	no
New Feature	no
RFC	no
QA	no

Description

Adds a special case for the IsISO3166Alpha2 and IsISO3166Alpha3 validators for Kosovo.

Kosovo declared independence in 2008, but we're still waiting for an official inclusion to the ISO3166 standard. In the meantime many official bodies have begun using the codes XK and XXK. An example of the prevalence of this unofficial usage is that that iOS lists XK as one of its locale codes.

Expected: IsISO3166Alpha2("XK") returns true
Actual: false

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This change is 

[sergeyglazyrindev]

Hello guys!
I forked this package cause owner disappeared. Hope, he will be back, but it would be easier to merge these changes back if he is back
Link to my repo: create issue there and we'll discuss it.