Development version of `KrigR`.

A first step towards removing rgdal dependency which keeps breaking the installation for users.

Manual Changelog:

Introduced functionality:
- CDownloadS() - an updated version of download_ERA() which supersedes the latter in a few key ways:
  - Full terra implementation
  - More efficient downloads and temporal aggregation
  - Metadata approach for input validation and future widened support of datasets hosted at CDS
- Miscellaneous helper functions to support CDownloadS()
Deprecated functionality (all of these will be made functional again in the next release):
- download_ERA()
- BioClim()
- download_DEM()
- krigR()

Reorganisation of CDS Storage of Era5-Land and Implementation of Forced Singular Download by @ErikKusch in #5
CDS Backend Issues for Forecast Data Sets by @ErikKusch in #6
Quality of Life Improvements by @ErikKusch in #7
First-hour fixes for 1950 by @ErikKusch in #8
Aggregation Speed Improvements & Monthly Ensemble Member Precipitation Fix by @ErikKusch in #9
Removal of Variable_List function by @ErikKusch in #10
Parallel Progress Bars by @ErikKusch in #11
Fixes to Source argument usage in pipeline call of krigR() as highlig… by @ErikKusch in #13
Fix for western-hemisphere extent issue that has CDS report extents f… by @ErikKusch in #14
Fix for 1-hour downloads by @ErikKusch in #15
download script throwing error: by @beatonan in #16

Full Changelog: https://github.com/ErikKusch/KrigR/commits/Dev