Implement system `bgnpcgn-fao-latn-latn-1968` (BGN/PCGN Roman-Script Spelling Convention -- Faroese (1968)

[ronaldtse]

This issue is to implement the transliteration system of bgnpcgn-fao-latn-latn-1968.

This system is referred in the GeoNames database as fao_Latn2Latn_BGN_1968, with the system title 'BGN/PCGN Roman-Script Spelling Convention -- Faroese (1968)'.

Tests should rely on the data extracted for the fao_Latn2Latn_BGN_1968 system in https://github.com/riboseinc/geonames-transliteration-data .

Metadata:

authority_id: bgnpcgn
id: 1968
language: iso-639-2:fao
source_script: Latn
destination_script: Latn
name: BGN/PCGN Faroese 1968 Roman-Script Spelling Convention Agreement
url: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/693794/ROMAN-SCRIPT_SPELLING_CONVENTIONS.pdf
creation_date: 1968

[ronaldtse]

Spec: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/693794/ROMAN-SCRIPT_SPELLING_CONVENTIONS.pdf

Similar to #154 #106 #86 there is an output character set condition.

[ronaldtse]

Done in #694.