New features
* Updated to support PyQuil v2.9.0 and PennyLane v0.4.0. Note that PennyLane-Forest now requires PennyLane>=0.4
* The observable `qml.Hermitian(A, wires)` can now be measured on an arbitrary number of wires. That is, you can now pass a matrix A of size `[2**N, 2**N]` which acts on `N` qubits (i.e., `len(wires)==N`).
* Adds support for the `qml.var()` measurement return type provided by PennyLane v0.4.