Update docs, add convenience implementations

[jssblck]

Overview

Update the docs for org_id to specify when users might see this and what they should do about it.

Also, I've added a few convenience things I've been wanting:

• Macros for static construction at compile time. No more Locator::parse(...).expect(...)!
• AsRef impls for all locators.
• FromStr impls for all locators, so now we can use str::parse.

Acceptance criteria

• Docs explain org_id better.
• Types in this package are easier to construct and use.

Testing plan

All changes, other than the doc changes, are covered with automated tests.

Risks

No real risk.

References

None.

Checklist

• I added tests for this PR's change (or explained in the PR description why tests don't make sense).

[JeffreyHuynh1]

The macros look great!. Thanks for updating the docs.

Was gonna suggest that we add a test(s) for the failure cases of the from_str impl, but because it's just calling parse I don't think that's necessary because those cases are already covered in the existing tests.

[JeffreyHuynh1]

This is really cool, didn't know about the impls macro