Add load.bash helper for standardized includes

[jacksgt]

This makes it easier to include the library with bats_load_library:

bats_load_library has two modes of resolving requests:
by relative path from the BATS_LIB_PATH to a file in the library
by library name, expecting libraries to have a load.bash entrypoint

https://bats-core.readthedocs.io/en/stable/writing-tests.html#bats-load-library-load-system-wide-libraries

Closes #52

[vincent-zurczak]

Hello!
Thank you for this contribution. There is another PR to fix the CI.
In the meantime, could you amend your commit and sign it please? It seems that we will not be able to merge your commit until it is signed.

[vincent-zurczak]

@jacksgt Can you rebase your branch from master please?
We updated the CI process.

[jacksgt]

@vincent-zurczak Done and done! Thanks for taking a look :-)

[vincent-zurczak]

Hello @jacksgt.
Github keeps on saying we cannot merge because « Commits must have verified signatures ».

Could you amend your commit once again and sign it please?
As a reminder, here is how to sign commits: https://docs.github.com/en/authentication/managing-commit-signature-verification/signing-commits

[vincent-zurczak]

Hello @jacksgt.
Any news about the signed commit? I know this is not convenient.