modular schema

[Benjmhart]

would be great to have an $include syntax, in the form:

$include <filepath> as x - to import the Start schema in that file as an an available schema under name x
$include x in <filepath> as y - to import the named schema in that file (x) as a different name (y)
$include x in <filepath> - to import the named schema in that file under its original name

this would allow for a good deal of code reuse, especially with the 'parameterized schema' feature request