Implement system `alalc-tir-ethi-latn-1997` (ALA-LC Romanization Table -- Tigrinya (1997 + 2011)

[ronaldtse]

This issue is to implement the transliteration system of alalc-tir-ethi-latn-1997.

This system is referred in the GeoNames database as tir_Ethi2Latn_ALA_1997, with the system title 'ALA-LC Romanization Table -- Tigrinya (1997)' and 2011.

• 1997: http://catdir.loc.gov/catdir/cpso/romanization/tigrinya.pdf
• 2011: https://www.loc.gov/catdir/cpso/romanization/tigrinya.pdf

Tests should rely on the data extracted for the tir_Ethi2Latn_ALA_1997 system in https://github.com/riboseinc/geonames-transliteration-data .

[ronaldtse]

Note that the all Tigrinya systems in the GNDB including tir_Ethi2Latn_ALA_1997 contain Thai data, not Tigrinya, likely a mistake of the encoder thinking that tir is for Thai (which is tha).

[ronaldtse]

Merged in interscript/maps#9.