Missing documentation for spline control

[marcpaterno]

While implementing a requested feature in Firecrown, I came across a missing bit of documentation.

Some of the parameters in include/core_ccl.h are not documented in https://ccl.readthedocs.io/en/latest/source/notation_and_other_cosmological_conventions.html#controlling-splines-and-numerical-accuracy

• A_SPLINE_MINLOG_SM
• A_SPLINE_NA_SM
• DLOGK_INTEGRATION
• DCHI_INTEGRATION