Url is special

[qsantos]

This closes #800 by exposing Url::is_special

[codecov[bot]]

Codecov Report

Patch coverage: 40.00% and project coverage change: -0.07 :warning:

Comparison is base (a4633be) 82.78% compared to head (5a7eddc) 82.71%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #826 +/- ## ========================================== - Coverage 82.78% 82.71% -0.07% ========================================== Files 20 20 Lines 3335 3339 +4 ========================================== + Hits 2761 2762 +1 - Misses 574 577 +3 ``` | [Impacted Files](https://codecov.io/gh/servo/rust-url/pull/826?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=servo) | Coverage Δ | | |---|---|---| | [url/src/lib.rs](https://codecov.io/gh/servo/rust-url/pull/826?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=servo#diff-dXJsL3NyYy9saWIucnM=) | `76.20% <0.00%> (-0.31%)` | :arrow_down: | | [url/src/parser.rs](https://codecov.io/gh/servo/rust-url/pull/826?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=servo#diff-dXJsL3NyYy9wYXJzZXIucnM=) | `81.59% <100.00%> (+0.02%)` | :arrow_up: | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=servo). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=servo)

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[qsantos]

I have addressed the new linting rules in https://github.com/servo/rust-url/pull/825. I'll avoid moving the fix to this PR since there is already a discussion there. I'll rebase once #825 is merged.