1.5.0

This introduces an incompatibility where the variable m is now a reserved keyword.

Added support for models with an optional argument.
This is extensively used in Zotonic for accessing (database) models.

The syntax to access more rsc is:

{{ m.rsc.foo.bar::42 }}

This will call the model_call function in the runtime as:

Runtime:model_call(rsc, [ <<"foo">>, <<"bar">> ], 42, Context).

The argument is optional:

{{ m.rsc.foo.bar }}

Calls the model as:

Runtime:model_call(rsc, [ <<"foo">>, <<"bar">> ], undefined, Context).