add notes on virtual/exported resources
notes on template testing
ensure that modulepath can take multiple directories
add support for multiarg fns (breaking change)

This commit adds support for multiarg functions. As a consequence, single argument functions,
which were previously stubbed using simple string keys in the stub map, must be wrapped into
a single-element array. eg where before you had:

{ :extlookup => {foo => bar}}

you now need:

{ :extlookup => {[foo] => bar}}