Add a function/closure analyzer

[Crell]

Description

Adds a new FunctionAnalyzer interface and FuncAnalyzer class for functions and closures.

Motivation and context

Functions can have attributes too, man!

Still to do:

• [ ] Docs
• [ ] Caching wrappers

Types of changes

What types of changes does your code introduce? Put an x in all the boxes that apply:

• [ ] Bug fix (non-breaking change which fixes an issue)
• [X] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)