PaleoCalAdjust v1.0: Paleo calendar-effect adjustments in time-slice and transient climate-model simulations

With the exception of several changes noted below, this is the repository that accompanies the paper: Bartlein, P. J. and Shafer, S. L.: Paleo calendar-effect adjustments in time-slice and transient climate-model simulations (PaleoCalAdjust v1.0): impact and strategies for data analysis, Geosci. Model Dev. Discuss., 2018, 1-36, https://doi.org/10.5194/gmd-2018-283, 2018. The programs implement an approach for adjusting for the "paleo calendar effect" -- the impact that the changes in the length of months or seasons over time (related to the changes in the eccentricity of Earth's orbit and to precession), have on the summarization of paleoclimatic model output. The current version of the key program is cal_adjust_PMIP.f90 (in the folder /f90), which applies the adjustment to CMIP5/PMIP3- or CMIP6/PMIP4-formatted files, and a related program, month_length.f90, that can be used to produce tables of the changing length of months over time. (The original main program cal_adjust_PMIP3.f90 was modified to accommodate CMIP6/PMIP4-formatted files.) Figures illustrating the paleo calendar effect are in the folder /figures, and relevant data sets for exercising the programs are in the folder /data. Several minor modifications to the main program cal_adjust_PMIP.f90 and its modules were made to accommodate CMIP6/PMIP4 files, the filenames of which contain an additional "grid_label" field not present in CMIP5/PMIP3 filenames: the main program cal_adjust_PMIP3.f90 and module CMIP5_netCDF_subs.f90 were renamed as cal_adjust_PMIP.f90 and CMIP_netCDF_subs.f90 respectivly, because they are now generic. No changes were made to CMIP_netCDF_subs.f90, and only minor changes were made to cal_adjust_PMIP.f90 to allow reading and writing of both CMIP5/PMIP3 and CMIP6/PMIP4 formatted files; the info file read by cal_adjust_PMIP.f90 (e.g. cal_adj_info.csv) was modified to include an "activity" field (either "PMIP3" or "PMIP4") and a "grid_label" field (blank for PMIP3 files); the paths to the "source" and "adjusted" netCDF files are now explicitly given in the info file, as opposed to being set in the main program