Pyddlib

Fixed
- Convert all terminal values to float type in ADD class

Added
- ADD class with factory methods for constructing terminals and variables
- ADD operator overloading for basic arithmetic manipulation (+, -, *, /)
- ADD unary minus (-) and unary negation (~) for variables
- ADD variable marginalization
- ADD string representation for debug

Added
- DD class implementing iterator over the structure of the the diagram
- DD operations reduce, apply and restrict
- BDD class with factory methods for constructing terminals and variables
- BDD operator overloading for basic boolean manipulation (AND, OR, NOT, XOR)
- BDD string representation for debug