New definition syntax

Magma provides an alternate (and preferred syntax) for defining circuits. This looks like

import magma as m

class Top(m.Circuit):
    io = m.IO(I0=m.In(m.Bit),
              I1=m.In(m.Bit),
              O=m.Out(m.Bits[2]))

    inner = InnerModule()
    m.wire(io.I0, inner.I)
    m.wire(inner.O, io.O[0])
    m.wire(io.I1, io.O[1])

This syntax differs from the original syntax in two main ways: * IO = ["name", type, ...] -> io = IO(name=type, ...) * The logic usually inside def definition() can now be inlined directly into the class-definition body. The ports normally accessibly through the attributes of the argument of this function can now be accessed as attributes of io.

Other than these minor changes (simplifications, really) to the definition syntax, the magma operates as before. In particular the syntax and semantics of wiring, instancing, and types have not changed.

Notes

• This change updates the standard to make this new syntax preferred to the old syntax. Additionally, we are also deprecating the factory functions DefineCircuit() and DeclareCircuit(); these will continue to work but we suggest against using these methods.
• There maybe some robustness issues with the isdefinition introspection method. If you encounter these, please file issues.