Replace gsl-lite with span-lite

[jcelerier]

For #28

[BurningEnlightenment]

I found some minor nits, but we'll need to wait for Niall's approval.

[ned14]

I pretty much agree with @BurningEnlightenment's feedback. Thanks for the PR!

[ned14]

@BurningEnlightenment Will this need some changes to the vcpkg port?

[github-actions]

Unit Test Results

    3 files  -  1    41 suites  -15   6m 56s ⏱️ - 2m 40s
  49 tests ±  0    49 ✔️ ±  0  0 💤 ±0  0 ✖️ ±0 
145 runs  -51  145 ✔️ -51  0 💤 ±0  0 ✖️ ±0 

results for commit e5414b7 ± comparison against base commit 568e181

[BurningEnlightenment]

Yeah, I'll take care of that. Will probably take a few days due to the review process, etc.

[jcelerier]

thanks ! :)

[BurningEnlightenment]

I fixed a minor build system issue and opened microsoft/vcpkg#25560

[ned14]

https://github.com/ned14/outcome/runs/7141879761?check_suite_focus=true suggests this PR broke Outcome CI?

[BurningEnlightenment]

I will take a look in an hour or so.

[BurningEnlightenment]

https://github.com/ned14/outcome/runs/7141879761?check_suite_focus=true suggests this PR broke Outcome CI?

This looks like an issue I already encountered while updating the vcpkg port (not #32). I pushed 9cdcd45 onto the master branch to fix it. So the CI should be green again next time.