Adds colourmaps from CET, Fabio Crameri and William Lenthe

[sebjameswml]

This PR contains lookup table based maps from Crameri and CET, along with William Lenthe's code to generate a number of other maps.

[sebjameswml]

There's an annoying array bounds issue coming from

template<typename Real, size_t N, size_t K, size_t D>
void UniformSpline<Real, N, K, D>::interpolate(const Real t, const bool clamped, Real * const pt) const {

in which the compiler decides that the code is going to attempt to access an array with index -3.

[sebjameswml]

There's a typo in Cmakelists. coloursmaps_crameri.h