Execution Engine

The backbone of Reilex is the symbolic execution engine.
The basic outline of symbolically executing a basic block is as follows:

1. Load state from before the first instruction is executed.*
2. Iterate over the REIL instructions in that basic block, at each step:
   a.Load the symbolic value of each operand from the current state
   b.Apply the REIL instruction**
   c.Update the state according to the results of the REIL instruction
   3.Upon reaching the end of the block, defer to the pathing strategy to determine next action.

*State consists of bindings between names of registers/memory addresses and an abstract syntax tree representing the symbolic value of the register/memory at the address. The implementation is simply a python dictionary such that the keys are names of registers/memory dresses and values are the abstract syntax trees.

**Implementation note: This is handled by a dictionary binding the names of operations to a pointer to a function that handles the operation. I believe this is a clean implementation, however it does require a separate function for each possible instruction. Since the semantics of REIL are so simple, this is acceptable.