The Big (incident only) Fix

[WillJRoper]

This PR is a monolithic fix of the incident spectra side of the repo. It is currently in draft as things progress but will track changes and list outstanding problems.

Changelog:

• The package is now restructured to allow installation. Installation is a necessity to have reusable tools which can be employed in multiple scripts and a) standardise the code and b) make writing scripts for different grids easier.
• Because of the above the package is now in "src structure".
• A Parser has been introduced which overloads argparse.ArgumentParser to implement some standard command line arguments for use across all scripts. This has been implemented in all scripts.
• GridFile now writes version and time metadata automatically and has been implemented in all scripts.
• A utilities module has been introduced to house the tools for use across the scripts.

Current status:

• BC03: ~FAILING~ WORKING - Fails on a regexp search returning None.
• BC03-2016: FAILING - download scripts download variants after updating (in this PR) but the code looks for files which don't exist in the 2016 data.
• BPASS 2.2.1: FAILING - hoki hasn't fixed the update_default_config astropy issue. This could be fixed by pinning the version but we should probably raise an issue on their end to have it fixed.
• BPASS 2.3: FAILING - see point above.
• Maraston: WORKING
• Maraston11: WORKING
• Maraston13: WORKING - I assume this works because the data is currently not online and public and @newmansoph had it working.
• Yggdrasil: ~FAILING~ WORKING - This script uses subprocesses to call wget which is not installed at any point or signalled that it should be so the data can't be downloaded.

TODO list:

• Get all scripts running.
• Fully sanitise the package structure.
• Move all utilities to the utilities module and adjust imports.
• Remove all unused imports.
• Document functions.
• Provide a generic downloader with requests
• Make scripts safer with unyt conversions instead of magic numbers.
• Introduce tests for tools.
• Introduce a cheap integration test.

Issue Type

• Enhancement

Checklist

• [x] I have read the [CONTRIBUTING.md]()
• [x] I have added docstrings to all methods
• [x] I have added sufficient comments to all lines
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no pep8 errors
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes

[WillJRoper]

Hoki issue raised here: https://github.com/HeloiseS/hoki/issues/99

[WillJRoper]

Hoki fix raised in this PR: https://github.com/HeloiseS/hoki/pull/100

[stephenmwilkins]

• BC03-2016, bpass2.2.1, and bpass2.3 all now work. However bpass requires manual download at the moment.

[sophie-newman]

found issues in some edits that were made to maraston13 - trying to fix these now