rel-2.0.8

The following changes were made in this release:

• Added optimizations for log(exp(x)), exp(log(x)), and exp(log1p(x))
• AdvancedIncSubtensor Ops (e.g. x[idx] = ...) can now be in-place optimized
• Sigmoid and Softplus have been moved to aesara.scalar.basic_scipy, and expit was added as an alias to sigmoid
• Added a Numba graph compilation backend and a NUMBA compile mode option (e.g. aesara.function(..., mode="NUMBA"))