Split package into ClassicalOrthogonalPolynomials.jl and OrthogonalPolynomialArrays.jl

[dlfivefifty]

Probably ClassicalOrthogonalPolynomials.jl should just be a streamlined package with the recurrence relationships, evaluation, and possibly the connection/differentiation matrices but without the ContinuumArrays.jl support.

[DanielVandH]

Could this just be an extension without needing another package? Maybe the extension itself would have more dependencies to work with the ContinuumArrays stuff anyway that it'd be annoying to manage compared to a separate package though.