Add Vatican IBAN support

[washeck]

Vatican IBAN format was added in IBAN Registry release 81
in December 2018.

All Changes

• Add an entry to the docs/changelog.rst describing the change.

• Add an entry for your name in the docs/authors.rst file if it's not
  already there.]

[codecov-io]

Codecov Report

Merging #355 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #355   +/-   ##
=======================================
  Coverage   95.93%   95.93%           
=======================================
  Files         157      157           
  Lines        3981     3981           
  Branches      523      523           
=======================================
  Hits         3819     3819           
  Misses         98       98           
  Partials       64       64

Impacted Files	Coverage Δ
localflavor/generic/validators.py	100% <ø> (ø)	⬆️

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[benkonrath]

Looks good. Thanks!