Fun with frequency domain

[khider]

1. Goal: Use the notebooks in the mathom drawer (to be renamed FreqFun) to create notebooks showcasing Pyleoclim capabilities.
2. Description: Use the existing notebooks and add the following Holocene notebook presented at EarthCube meeting
3. References/data sources:
4. Keywords (science): spectral analysis, wavelet analysis, cross-wavelet analysis
5. Keywords (tech): Pyleoclim, pylipd