Fix invalid output or crashes when calling a mixin which takes variable arguments from another mixin *also* taking variable arguments when no arguments are passed in
Rework variable argument support to support named arguments. This requires altering arglists to store Arguments instead of the previous approach of just wrapping the passed-in Expression values, and includes changes to other functions to cope with the resulting Lists or ArgLists as appropriate
Merge pull request #219 from rowanbeentje/improvevariableargumentsupportv2

Improve variable argument support