Allow integer values for a Cookie() name

[nosilver4u]

Fixes #845 so that an exception isn't thrown for legitimate numeric cookie names.

There are two changes:

1. Modify the check for $name, to allow both string and integer cookie names.
2. Change the exception thrown to indicate a string OR int is permitted.

Pull Request Type

• I have checked there is no other PR open for the same change.

This is a:

• Bug fix

Context

Currently, multiple plugins, and possibly even WP core are throwing errors if someone has a cookie with a numeric name. Would love to see this issue go away, so that folks don't have to resort to deleting cookies in the dev tools of their browser.

Quality assurance

• This change does NOT contain a breaking change (fix or feature that would cause existing functionality to change).
• I have commented my code, particularly in hard-to-understand areas.
• I have added unit tests to accompany this PR.
• The (new/existing) tests cover this PR 100%.
• I have (manually) tested this code to the best of my abilities.
• My code follows the style guidelines of this project.

[jrfnl]

@nosilver4u Aside from the fundamental question of whether this is a valid "fix" (in contrast to the user doing it wrong), a PR will not be reviewed or even considered without unit tests documenting the use case. So without tests, this PR will be closed.

[nosilver4u]

I missed an update to the parse() method anyway, so I need to create a new pull request with both changes.
Regarding tests, I had wondered about that, so I'll see what I can figure out on that end.