Support pt2 pt5

[LBeaudoux]

• add attribute indexing (e.g. you can call Lang("fr")["name"] in addition to Lang("fr").name)
• allow instantiation with one or multiple compatible keyword arguments (e.g. Lang(pt1="fr", pt3="fra"))
• expand ISO 639-2 support to languages not covered by ISO 639-3
• add ISO 639-5 support
• improve representation of Lang
• remove JSON mapping file from repo