Dataframe attributes should return standard variable information

[khider]

Have a look at this table: https://www.ncei.noaa.gov/pub/data/paleo/contributions_by_author/clemens2021/clemens2021-u1446-tex86hsst-noaa.txt

The variable information is:

Which takes into consideration the standard names of the variables and other information. Right now, the attributes only contain the column header as variable names:

We need to store the rest of the information from the NOAA API, using their dictionary structure:

The way it is done in PyLiPD is to use the column name as the key (instead of 1) and store the rest of the information in a nested dictionary. So we should get something like:

{"variables":{"Hole":{"cvDataType":"PALEOCEANOGRAPHY", "cvWhat":"sampling metadata->sample identification"}}

null should be None to stay with Python

[khider]

Let's hold off on that one since #5 actually provided similar functionality