Add z-changelog; replacement for scripts/Get-Changelog.ps1

[BillyONeal]

• Built on the 'bones' of portsdiff
• Also implemented the single pass algorithm for portsdiff
• Fixed bad newlines in portsdiff:

• Removed the version numbers for the 'removed' ports output because the version at the previous snapshot is meaningless; the meaningful version would be the last version but we don't know that.

[ras0219-msft]

This seems likely to cause a mistake (forget to fill in the correct final table); I'd drop it.

edit: suggestion is to drop this specific step. Leave the table empty (or nonexistent) until the final numbers are ready.

[BillyONeal]

Are you saying to drop the table entirely? I think @AugP said he liked the table...

[data-queue]

May be out of scope for this PR. Are there tests for portsdiff? I feel like we need to add them if not: portsdiff is not an experimental command, which means it should be supported on all platforms. I was not able to get portsdiff working on Linux locally.

[BillyONeal]

May be out of scope for this PR. Are there tests for portsdiff? I feel like we need to add them if not: portsdiff is not an experimental command, which means it should be supported on all platforms. I was not able to get portsdiff working on Linux locally.

I agree tests would be good but I don't have great ideas on doing so :/

[BillyONeal]

May be out of scope for this PR. Are there tests for portsdiff? I feel like we need to add them if not: portsdiff is not an experimental command, which means it should be supported on all platforms. I was not able to get portsdiff working on Linux locally.

[DEBUG] 1001: execute_process(/usr/bin/git --git-dir=/home/bion/vcpkg/.git --work-tree=/home/bion/vcpkg -c core.autocrlf=false cat-file -t HEAD)
[DEBUG] 1001: cmd_execute_and_stream_data() returned 0 after     1479 us
[DEBUG] 1002: execute_process(/usr/bin/git --git-dir=/home/bion/vcpkg/.git --work-tree=/home/bion/vcpkg -c core.autocrlf=false cat-file -t HEAD~10)
[DEBUG] 1002: cmd_execute_and_stream_data() returned 0 after     1371 us
[DEBUG] 1003: execute_process(/usr/bin/git --git-dir=/home/bion/vcpkg/.git --work-tree=/home/bion/vcpkg/ports-HEAD -c core.autocrlf=false checkout HEAD -f -q -- ".\\ports" .vcpkg-root)
[DEBUG] 1003: cmd_execute_and_stream_data() returned 1 after     4097 us
[DEBUG] 1004: execute_process(/usr/bin/git --git-dir=/home/bion/vcpkg/.git --work-tree=/home/bion/vcpkg/ports-HEAD -c core.autocrlf=false reset)
[DEBUG] 1004: cmd_execute_and_stream_data() returned 0 after    14753 us
[DEBUG] 1005: execute_process(/usr/bin/git --git-dir=/home/bion/vcpkg/.git --work-tree=/home/bion/vcpkg/ports-HEAD~10 -c core.autocrlf=false checkout HEAD~10 -f -q -- ".\\ports" .vcpkg-root)
[DEBUG] 1005: cmd_execute_and_stream_data() returned 1 after     4810 us
[DEBUG] 1006: execute_process(/usr/bin/git --git-dir=/home/bion/vcpkg/.git --work-tree=/home/bion/vcpkg/ports-HEAD~10 -c core.autocrlf=false reset)
[DEBUG] 1006: cmd_execute_and_stream_data() returned 0 after    14850 us

Looks like there's a \\ that needs to be / here