Extend AST for logic formulas with spatial logic operators

[Yurand2000]

A new set of logic operators needs to be included in the analysis tool:

• Empty Heap empH No memory is allocated.
• Memory State x -> a where x is a variable and a an arithmetic expression. The memory pointed by x has the value a x -> _ where x is a variable. The memory pointed by x is allocated.
• Separation And P * Q where P and Q are logic formulas. There exists a disjoint partition of heap memory h1, h2 which verifies the formula P on heaplet h1 and formula Q on heaplet h2.

[Yurand2000]

A note on the previously mentioned logic operators (some to remove, some to add):

• Memory State x -> _ is actually equal to ∃v. x -> v, so the second case is useless.
• Memory Deallocated x -/> which represents that the memory pointed by x has been deallocated.