Waveform: add doxygen comment documenting AlignTo

no paper reference yet, only a handwavy explanation of what it does.
Waveform: add code to allow selection of non-spinning T4 approximant
WaveformAligner: check interval passed to constructor

we implictly used that t1<t2 and now actually check for this. Also abort
if search inside of T() array runs out of bounds.