Added Serbian language (latin script)

[goksiii]

Added support for a latin script for the Serbian language.

[jenssegers]

The filename change will break existing installations though. What are the official language codes for both of these?

[goksiii]

For the filename, I have used RFC 5646 (https://tools.ietf.org/html/rfc5646) document. I built filenames for both of these with standardization that is defined in mentioned document. Official language codes for both of these is "sr", by ISO 639-1. In ISO 639-2 document, the language code for the Serbian language may have 2 or 3 characters, "sr" or "srp".
I may add a latin version of Serbian language in this format "srp_Latin". What do you mean about this?

[goksiii]

Or I may use "sr_Latin" for the filename for a latin script version of the Serbian language. The filename for Cyrillic script version will stay same.

[goksiii]

@jenssegers any information about merging this pull request? are you ok with changes that I made on PR? I need the latin script of Serbian language in my project.

[jenssegers]

This page mentions some other possibilities: http://www.lingoes.net/en/translator/langcode.htm

sr-BA	Serbian (Latin) (Bosnia and Herzegovina)
sr-BA	Serbian (Cyrillic) (Bosnia and Herzegovina)
sr-SP	Serbian (Latin) (Serbia and Montenegro)
sr-SP	Serbian (Cyrillic) (Serbia and Montenegro)

Any chance we could use one of these?

[goksiii]

@jenssegers
Yes.
Filename of a Cyrillic script will stay same (only "sr.php"), but filename of a Latin script will be "sr-SP.php".

[goksiii]

@jenssegers
PR is updated with changes. Can you review again this PR?
Thanks :)