Add support for expressions

[leonardt]

• [x] Define supported expressions and syntax (should correspond to CoreIR primitives)
• [x] Implement a rewriter that changes functions containing expressions into Magma+Mantle code
• [x] Preserve metadata about original expressions for magma related errors

Primitive Operations

Arith

• [x] op1 + op2
• [x] op1 - op2
• [x] carry(op1 op op2, in=None, out=None) Will defer until we can define good syntax
• [x] trunc(op1 op op2) Will defer until we can define good syntax
• [x] - op1
• [x] op1 >>> op2 Arithmetic shift Syntax not supported by Python

Logic

• [x] op1 & op2
• [x] op1 ~& op2 Syntax not supported by Python
• [x] op1 | op2
• [x] op1 ~| op2 Syntax not supported by Python
• [x] op1 ^ op2
• [x] op1 ~^ op2 Syntax not supported by Python
• [x] op1 >> op2
• [x] op1 << op2
• [x] ~ op1
• [x] reduce(op, op1) Can be implemented using function syntax
• [x] not op1 can be implemented as ~ reduce(or, op1)
• [x] op1 and op2 (Logical And)
• [x] op1 or op2 (Logical or)
• [x] op1 == op2

Misc

• [x] value[slice]

[phanrahan]

These seems like good set of ops.