feat(get_modflow): support modflow6 repo releases

[wpbonelli]

Supports installing releases from the main modflow6 repository. Updates the repo option to accept modflow6 so the user can select any of the following:

• executables (default)
• modflow6
• modflow6-nightly-build

The modflow6 repo's release archive contains most of the repository, not just binaries, so instead of unzipping directly to bindir like the other 2 options, there is an extra step to unzip in the download location before copying binaries to bindir.

Adds a section describing repo selection to the docs. Also adds a table of contents.

Motivation

Besides covering the bases as far as distributions go, this is a step towards replacing the pymake dependency in modflow6 tests (currently pymake is used to download the latest mf6 release, among other things)

[codecov]

Codecov Report

Merging #1573 (ef590eb) into develop (a0ca344) will increase coverage by 0.1%.
The diff coverage is 95.2%.

@@            Coverage Diff            @@
##           develop   #1573     +/-   ##
=========================================
+ Coverage     72.5%   72.6%   +0.1%     
=========================================
  Files          251     251             
  Lines        54293   54423    +130     
=========================================
+ Hits         39377   39542    +165     
+ Misses       14916   14881     -35     

Impacted Files	Coverage Δ
flopy/utils/get_modflow.py	54.7% <95.2%> (+4.8%)	⬆️
flopy/mf6/data/mfdataarray.py	62.3% <0.0%> (-1.2%)	⬇️
flopy/utils/datautil.py	63.4% <0.0%> (-0.5%)	⬇️
flopy/mf6/data/mfdatalist.py	72.9% <0.0%> (-0.2%)	⬇️
flopy/mf6/mfpackage.py	64.3% <0.0%> (+<0.1%)	⬆️
flopy/mf6/data/mfdatastorage.py	70.6% <0.0%> (+1.2%)	⬆️
flopy/plot/map.py	83.9% <0.0%> (+1.5%)	⬆️
flopy/mf6/data/mfdatautil.py	54.3% <0.0%> (+1.6%)	⬆️
flopy/mf6/data/mffileaccess.py	66.0% <0.0%> (+2.1%)	⬆️
... and 1 more

[jdhughes-usgs]

Or it can append new or modify existing entries in code.json. We probably need to harmonize the attributes/keys in the code.json files.

[wpbonelli]

this can be removed later if future modflow6 releases use the same naming conventions for platform-specific zip files as the executables and nightly-build repos

• mac.zip
• linux.zip
• win64.zip

[mwtoews]

I've pushed a commit for a few changes. Roll back or comment anything that you disagree with. Here are my notes from my commit message:

• evaluate files to extract (rather than extracting to dowloads_dir)
• avoid div/0 with columns_str (with items longer than 79 chars)
• change asset dst_fname for modflow6
• prevent "--repo modflow6 --ostag win32" from succeding

[wpbonelli]

@mwtoews thanks for the review and fixes

My motivation for extracting the whole release instead of select files, besides not being sure which would be a less surprising option for the user, was because modflow6 tests need to download the latest release and rebuild it — currently this is done with pymake.download_and_unzip but I thought to replace it with get-modflow (with the wider goal of moving testing/miscellaneous utils to modflow-devtools and paring down pymake)

If this seems like a separate capability that doesn't belong here, the modflow6 tests could just pull in download_and_unzip from modflow-devtools instead After some thought this seems best. Downloading the repo for dev/testing doesn't seem like a concern of flopy's