misc fixes

[jeffreyhanson]

• Remove rgdal package dependency
• Updates URLs
• Update functions for downloading preprocessed data from Zenodo

[codecov]

Codecov Report

Merging #51 (b37e246) into master (85bdd0c) will decrease coverage by 0.18%.
The diff coverage is 83.87%.

❗ Current head b37e246 differs from pull request most recent head 66aa633. Consider uploading reports for the commit 66aa633 to get more accurate results

@@            Coverage Diff             @@
##           master      #51      +/-   ##
==========================================
- Coverage   97.63%   97.46%   -0.18%     
==========================================
  Files          44       44              
  Lines        2922     2919       -3     
==========================================
- Hits         2853     2845       -8     
- Misses         69       74       +5     

Files	Coverage Δ
R/plot_spp_aoh_data.R	99.01% <100.00%> (+0.05%)	⬆️
R/plot_spp_frc_data.R	100.00% <ø> (ø)
R/misc_zenodo.R	89.36% <80.00%> (-10.64%)	⬇️