Localflavor Sri Lanka: Support for Sri Lanka added in django-localflavor

[skdishansachin]

**Support for Sri Lanka Added as requested by this issue #491 **

What Fields are added ?

• Field for provinces of Sri Lanka.
• Field for districts of Sri Lanka.
• Field for Postal Code of Sri Lanka.

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.

New Fields Only

• Prefix the country code to all fields.

• Field names should be easily understood by developers from the target
  localflavor country. This means that English translations are usually
  not the best name unless it's for something standard like postal code,
  tax / VAT ID etc.

• Prefer 'PostalCodeField' for postal codes as it's
  international English; ZipCode is a term specific to the United
  States postal system.

• Add meaningful tests. 100% test coverage is not required but all
  validation edge cases should be covered.

• Add .. versionadded:: <next-version> comment markers to new
  localflavors.

• Add documentation for all fields.

[claudep]

@benkonrath Do you think you could find some time in the near future to review this request?

[benkonrath]

@claudep Yeah. I'll try to dedicate a few hours to going through the PR backlog a bit in the next day or two. Thanks for the reminder.

[claudep]

@skdishansachin Please fix the test failures!

[skdishansachin]

Okay I will fix those test failures @claudep

[benkonrath]

@skdishansachin Please fix the tests and then I'll take a look at this PR. I don't know why I have to continually approve the test runs but I'll be quicker about doing this now that I know that they need to approved more than once.

[skdishansachin]

@benkonrath @claudep Hey, sorry about sending that review request before fixing the issues properly. I'll check it soon when I have time. Thanks!

[benkonrath]

No problem. There's no direct feedback since I have to approve and run the tests in github CI... and I haven't been on top of that. That makes it harder for you to know that things aren't working correctly. This PR is on my radar now and hopefully we can make some progress soon. 🚀

[benkonrath]

I fixed the tests and implemented a few cleanups / improvements. I think it's good to go.

[skdishansachin]

@benkonrath Thanks for all the tweaks you made to get this working! Sorry for leaving this pull request hanging. I got caught up in my studies and exams. I checked out the changes you made, and they look great. I really appreciate it!

[benkonrath]

@skdishansachin No problem. Thanks for looking over my changes.