Metadata-rich Series

[CommonClimate]

LiPDSeries is on its way out, but Series is a very skinny format. Some say there is need for a Pyleoclim class that contains more metadata than Series, but isn't as bloated as LiPDSeries? In particular, depth would enable analyses of accumulation rate, hiatuses, etc, which are not possible without a data structure that accommodates it.

Another option is to keep what is now LiPDSeries, but be branded more generally (like "PaleoSeries"), and remove assumptions about LiPD structure. It would still require standard terminology, however, and LiPD/PaCTS/PaST seems the natural template for that terminology.

[CommonClimate]

addressed in #326