The capital of St. Vincent and the Grenadines is suitably busy, in a colorful Caribbean sort of way. The streets in front of the Public Market surge with impromptu vendors hawking a fragrant variety of fruits and vegetables. The dark, Gothic St. Mary’s cathedral is a 19th century addition. The Botanic Gardens is the oldest in the Caribbean, begun in 1765. Climb the hill to the 1806 Fort Charlotte,…