feat(builder): Set/Append Actions

This round out the new style actions and allow us to start deprecating
occurrences.

As part of ...

feat(parser): SetTrue/SetFalse/Count Actions

feat(builder): Expose ArgAction

Now that we can store constants for flags, we can apply defaults for
flags too.

Fixes #3294

This is the minimum set of actions for the derive to move off of
`parse`. These are inspired by...

refactor(parser): Extract Actions from Parser

This fixes a compatibility issue introduced in 9805fdad1b17fde2f5860969de84d7eb4d8f2b51

My hope is to add group actions as well, so we need to qualify what kind
of action this is.

If we felt this was important long-term, we should fix this outside of
the Action. Since we mig...

This changes how occurrences and values are grouped for multiple values.
Today, it appears as a ...

docs(derive): Make raw attribute more discoverable

Based on feedback in #3189

When creating `PendingValues`, I can't have the lifetime. I could make
it a `Cow` but decided t...

There is a default_missing_vals case which is slightly different because
its not actually a defa...

fix(parser): Make behavior more consistent

Especially important is not inferring intent from occurrences as
hopefully that will change with...

Before, if we were in trailing values that aren't delimite, we wouldn't
respect this flag and en...

I wrote these tests expecting to highlight a bug but it turns out things
were structured just ri...

fix cargo.toml link

Doesn't make sense to respect how the command line ended

Fixes #3761

We were independently starting occurrences and starting value groups.
Now we do them at the same...

Inferred flags can make it hard for a future action to trigger behavior
off of the selected alia...

fix: Remove deprecation warning

This is a step towards user-visible actions

refactor(parser): Remove dead code

fix(validator): Deprecate validator_regex

Fixes #3743

feat(parser): Allow people to plug into 'value_parser' macro

For most users, this won't be worth doing, they can just specify the
parser if needed. Where th...

fix: Deprecate value_parser predecesor

`validator_regex` is being ignored for now as I await on a comment
period for #3743

fix(parser): Improve panic messages for get_one, etc

fix(parser): Simplify the common getter API

Clap has focused on reporting development errors through assertions
rather than mixing user erro...

fix(parser): Switch to concrete iterators

fix(parser): Clean up remove types

The remove functions no longer return `Arc` but the core type, at the
cost of requiring `Clone`....

fix(parser): Increase compatibility between old/new approach

When to show usage? We are currently mixed about it. For `validator`,
we didn't show it at all...

feat(derive): Allow users to opt-in to `ValueParser`