Implemented gettext functions

[ArmorDarks]

singular

• [x] gettext( key )

plural

~~https://github.com/zaach/jsxgettext/issues/51~~

• [x] ngettext( singular_key, plural_key, value )

domain

https://github.com/zaach/jsxgettext/issues/94

• [ ] dgettext( domain, key )
• [ ] dngettext( domain, singular_key, plural_key, value )

context

https://github.com/zaach/jsxgettext/issues/94

• [ ] pgettext( context, key )
• [ ] npgettext( context, singular_key, plural_key, value )

domain and context

https://github.com/zaach/jsxgettext/issues/94

• [ ] dpgettext( domain, context, key )
• [ ] dnpgettext( domain, context, singular_key, plural_key, value )

category

• [ ] dcgettext( domain, key, category )
• [ ] dcngettext( domain, singular_key, plural_key, value, category )
• [ ] dcnpgettext( domain, context, singular_key, plural_key, value, category )

I hope that will help to have better view of project state.

[BYK]

Great work, thanks a lot!