Load a collection of Ragtime migrations from a directory. These can be in edn
or SQL format.

Given an collection of files with the same extension, return a ordered
collection of migrations. Dispatches on extension (e.g. ".edn"). Extend
this multimethod to support new formats for specifying SQL migrations.

Load one or more migrations from an edn reader source. Returns an ordered
collection of migration maps.

Load a collection of Ragtime migrations from a classpath prefix. These can be
in edn or SQL format.