Add LinkDirectory for directory path

[Liryna]

Call LinkDirectory when pdbPath is a directory Cache sourceFilesList for option -a

Checklist

• [ ] I have included examples or tests
• [ ] I have updated the change log
• [x] I am listed in the CONTRIBUTORS file
• [x] I have cleaned up the commit history (use rebase and squash)

Changes proposed in this pull request:

See https://github.com/GitTools/GitLink/issues/191

[Liryna]

Hi @GeertvanHorrik ,

Thank you for your review. I have made the two changes 👍

edit: Got error: Linker.cs(34,46): error SA1306: Field 'SourceFilesList' must begin with lower-case letter So I changed by starting with a _

[GeertvanHorrik]

Looks great, thanks for contributing!

[GeertvanHorrik]

Published 3.2.0-unstable.27.build.132 to chocolatey & nuget.