Add agegrid CLI

[cpalfonso]

The new gplately agegrid (or gplately ag) command will take a list of input files, a start and end time, and an output directory to create seafloor age and spreading rate grids. For full usage, see below:

usage: gplately agegrid [-h] [-c CONTINENTS_FILE [CONTINENTS_FILE ...]] [-r RESOLUTION] [--refinement-levels LEVELS] [--ridge-sampling RESOLUTION]
                        [--initial-spreadrate SPREADRATE] [-e MIN_TIME] [-s MAX_TIME] [-j N_JOBS] [-f NAME] [-u]
                        INPUT_FILE [INPUT_FILE ...] OUTPUT_DIR

Create age grids for a plate model.

positional arguments:
  INPUT_FILE            input reconstruction files
  OUTPUT_DIR            output directory

options:
  -h, --help            show this help message and exit
  -c CONTINENTS_FILE [CONTINENTS_FILE ...], --continents CONTINENTS_FILE [CONTINENTS_FILE ...]
                        input continent files
  -r RESOLUTION, --resolution RESOLUTION
                        grid resolution (degrees); default: 0.1
  --refinement-levels LEVELS
                        mesh refinement levels; default: 5
  --ridge-sampling RESOLUTION
                        MOR sampling resolution (degrees); default: 0.5
  --initial-spreadrate SPREADRATE
                        initial ocean spreading rate (km/Myr); default: 75
  -e MIN_TIME, --min-time MIN_TIME
                        minimum time (Ma); default: 0
  -s MAX_TIME, --max-time MAX_TIME
                        maximum time (Ma); default: 0
  -j N_JOBS, --n_jobs N_JOBS
                        number of processes to use; default: 1
  -f NAME, --file-collection NAME
                        file collection name (optional)
  -u, --include-unmasked
                        create unmasked grids in addition to masked ones