Merge pull request #30 from naviator/master

Need to start timer after creating it.
fixes issue #33
"optionally" swallows parameters when target function uses ...rest parameter
https://github.com/CodeCatalyst/promise-as3/issues/33

Implemented as proposed by John Yanarella: try to invoke with all given
parameters and only slice to function's length if that fails with an ArgumentError.
Merge pull request #34 from fwienber/issue-33

fixes issue #33