Implemented gettext functions

[ArmorDarks]

singular

• gettext( key )

plural

#51

• ngettext( singular_key, plural_key, value )

domain

#94

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

context

#94

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

domain and context

#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!