Update usage string for recombinationXe (no longer returning matter temperature)
Document type = Photon/Baryon option
Add method = NIntegrate / NDSolve option to internal buildFunction (does not do anything yet)
Implement alternative NDSolve method for internal buildFunction (NIntegrate is still the default)
Make NDSolve the default method for buildFunction and increase default pointsPerDecade from 50 to 200 for opticalDepthFunction
Do not plot buildFunction integrand by default
Limit automatic step size in buildFunction integration
Lower cross over point to avoid extrapolation warnings (not sure why this is necessary though)
Add constrainedXi2 that implements eqn (2.14) of baofit paper
Add constrainedXi4