Takes an ordered collection of migrations, and compiles the migrations using
vector syntax into SQL. This replaces the :do key with the :up and :down keys
on each affected migration. For example:

    [{:id "x" :do [[:create-table t [id "int"]]]}]

Is converted into:

    [{:id "x" :up ["CREATE TABLE t (id int)"] :down ["DROP TABLE t"]}]

Transactions may also be supplied as raw vectors, in which case an id will be
auto generated:

    [[:create-table t [id "int"]]]

This function is called automatically by ragtime.sql/load-migrations.