Param tags doc

[psprint]

Description

Document param'var→val' ice, alt-shift-q tags browser and also improve it.

Motivation and Context

I've recalled some undocumented features.

Types of changes

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

Checklist:

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

[vladdoster]

Please rebase your branch.

[psprint]

@vladdoster: I've rebased and fixed conflicts, please merge.