v3 migration

[Randy]

Migration to v3 is a work in progress, the majority of the v3 api is already exposed in v2.4, those should be finished first:

• Pair API (replaces trait API)

• event/event[] instead of phase for systems/triggers

• ecs.observer()

• ecs.term_iter(), ecs.term_next(), etc.

• Update ecs.query() to accept a filter or more of the ecs_query_desc_t fields

• Update ecs.system() the same as way as above

• Update ecs.trigger() to accept a term

• Update ecs.observer() to accept a filter

Breaking changes

flecs-lua will target v2.4 until v3 becomes stable (or at least until a beta release)

• Remove/replace deprecated functions, ecs_iter_t fields

• add_owned() -> override()

• Switch to the new builtin meta module

• Update constants / builtin components

Misc

• ecs_lua_query_next() -> ecs_lua_iter_next()

• ecs.iter_next()

• Consider dropping all other ecs.*_next() functions

• Consider re-adding the range checks to flecs-lua from the old meta module

• Expose JSON module

• System status callback

• Consider v2.4-style API for systems, entities, etc