Added support for mocking functions inside of modules

I think I've managed to add the ability to mock functions that are used inside of modules. 
I've shown what I aim to do with tests of course.

I've implemented the feature with a possibility to add a ```-Module``` switch parameter to the Mock function. (optional of course)

It's a bit tricky to deal with scopes and modules but I think that I've managed to get i right by:

1. Exporting all the functions from the module (this can be limited by using a condition anyway)
1. Importing the module with the -global (or -scope global in v3) switch ```Import-Module $module -Scope global```
1. The functions that you aim to mock need to be declared as global in the module (the export will limit this anyway if you want it to)
1. Finding and mocking the functions in the global scope by adding the -module switch to the mock function call.