Support "EXPLAIN QUERY PLAN"

[LostKobrakai]

In sqlite EXPLAIN QUERY PLAN … and EXPLAIN … return different values. Currently only the latter is supported with Repo.explain(:all, query), but I'd expect that the first one is actually the more common need, why people reach for explain. I think both options should be available (as enabled via the opts), but I think EXPLAIN QUERY PLAN should be the default, rather than just EXPLAIN.

[LostKobrakai]

It would also be great if aliases and parameters could be replaced in the result. I'm not sure how involved this is though.

[warmwaffles]

It's a pretty quick add

ecto_sqlite3/lib/ecto/adapters/sqlite3/connection.ex

Lines 657 to 659 in edef95f

	def build_explain_query(query) do
	IO.iodata_to_binary(["EXPLAIN ", query])
	end