[DNM] feat: delete multiple plugins at once

[vladdoster]

Description

• zinit delete command can delete multiple plugins at once
• remove broken symlinks after deleting a plugin
• improve option parsing (i.e., --all and --clean are mutually exclusive, don't default to deleting snippets)
• track number of failed deletions

Motivation and Context

Increase usability and reduce duplicate tasks.

Closes #239

Related Issue(s)

Usage examples

How Has This Been Tested?

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [X] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [ ] My change requires a change to the documentation.
• [X] I have updated the documentation accordingly.
• [X] I have added tests to cover my changes.
• [X] All new and existing tests passed.

[pschmitt]

Why are you always opening MRs twice?

[pschmitt]

Uh?

[vladdoster]

@pschmitt,

I merged the branch into the dedicated branch that Github will create if it is linked to an issue.