Create 36.test.ts (ffMathy#40)

Added SubstituteOf as as return type from Substitute.for (ffMathy#37)

Update package.json

allow limited multiple returns (ffMathy#31)

Refac function argument recording. fixes ffMathy#25, ffMathy#23 (ffMa…

…thy#30)

* refac function call args, fixes ffMathy#25 and ffMathy#23

* support optional args

added test for issue 23.

fix for bug where arg.is was called twice.

minor fix.

elaborated strict mode.

fixed issue ffMathy#18.