Check the parameter names to ensure there are no duplicates after parsing a route

[gameldar]

Description

After parsing a route go through the parameter names to ensure there aren't duplicates. If there are panic so we abort at initial creation.

Note this changes the add method to now return a Result (so warning will be produced with existing usage about an unused return value).

Motivation and Context

Closes #34

How Has This Been Tested?

Unit tests exist for the new conditions

Types of changes

• 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:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[gameldar]

Not sure if we want to do this as is (original commit enforced a panic instead... which again is undesirable for a library crate) - it does introduce a return value for the add method. Alternatively we could introduce a add_and_validate (or something like that) that allow you to choose to validate the names and potentially deprecate the old implementation?

[Nemo157]

One idea would be to add a builder, so you would add routes to the builder then get the Router back when you finalize it. That would allow delaying the error from the add method to a finish method, so you only have to deal with a Result in one place (presumably by expecting it in most uses).

Alternatively, there could be two add methods, maybe an add_checked that returns a Result and have add just unwrap that result, so if users were dynamically loading their routes they would have the option of dealing with errors in them, while most users with statically defined routes will just get a panic if they screw one up.