Language Extension Specification Docs

[amccaskey]

We need a place to point people to detail the language extension specification.

I'm thinking the following topics need to be detailed:

• Introduction
• Memory Model
• Execution Model
  • retargetable
  • multi-modal (nisq, ftqc)
• Programming Model
  • quantum kernels
  • modifiers on kernels (observe, adjoint, ctrl, etc.)
  • Classical control flow
• Qubits and Qregs
  • API on Qreg
• Quantum Instructions
  • Available instructions
  • Instruction modifiers
  • Instruction broadcasting
• Closures and Callables
  • lambdas and kernelsignature
• Common Patterns
  • Compute Action
• Variational API
  • optimizers, optfunction, ObjectiveFunction

Throughout we'll provide examples in C++ and Python.