vapi: Update enchant.vapi for Enchant 2.x
Add deprecations and new methods.
[I am the upstream maintainer of Enchant!]
I have added the new 2.x top-level API set_prefix_dir.
I have added Dict.add and Dict.is_added (which are really old!) and deprecated Dict.add_to_pwl and Dict.is_in_session.
I have added Dict.free_string_list, Dict.get_extra_word_characters, and Dict.is_word_character (with associated enum WordPosition, which isn't present in enchant.h, as that just uses numbers).
I have added Dict.remove, Dict.remove_from_session and Dict.is_removed.
I have reordered some methods to make the VAPI file more closely match the C header, for ease of maintenance.
Outstanding problem: Dict.store_replacement's string length arguments should work like Dict.add etc., that is, they should default to -1; but of course this is impossible given the current argument order. It would be nice to find a fix for this.