Remove hard-coded number of Chebyshev polynomial coefficients in ChebHash

[kernelmethod]

ChebHash currently computes an order-1024 discrete Chebyshev transform for all inputs. This defeats the purpose of ChebHash in the first place, which is to generate a variable-size transform so that we can achieve a desired accuracy without having to generate more coefficients than necessary. The current hardcoded number of coefficients should be replaced with a method for figuring out how many coefficients should be generated for a given input function f.

[kernelmethod]

This was partially addressed in 9590d8c by allowing users to specify the number of coefficients explicitly. There still isn't any support for automatically choosing the number of coefficients, though.

[kernelmethod]

Closed as a result of #26.