Adds a new subdirectory `interfaces` where standard interfaces
are defined. Additional interfaces for a given operation can
be added with an `AliasOf` type operator. Provides type
operators that give the return type, full function type, and
the type of a dependency on, a given operator.
Resolves#6.
Co-authored-by: Glen Whitney <glen@studioinfinity.org>
Co-authored-by: Jos de Jong <wjosdejong@gmail.com>
Reviewed-on: #8
