feat(http/unstable): add capability to attach handlers by methods, implement sensible defaults

[kerezsiz42]

Hi everyone!

I would like to propose a new implementation of the route() function that adds the capability to define handlers on a per-method basis (in a style similar to Fresh) or to use a single handler that handles all methods.

I envision the route() function being used only once when we pass it to Deno.serve(). In the case of a REST API, one would:

• Export an array of routes in user.ts with URL patterns such as /api/users and /api/users/:id.
• Export an array of routes in products.ts with URL patterns such as /api/products and /api/products/:id.
• Import these in main.ts, then call Deno.serve(route([...userRoutes, ...productRoutes, notFoundRoute], errorHandler)).

The current defaultHandler() does not seem very useful, as a wildcard route can provide the same functionality (see tests). I believe an optional errorHandler() would be more important.

While my PR adds some logic to the route() function, it conforms to the relevant specifications (RFC2616) and practices regarding the "Method Not Allowed" response, error handling, and the default "Not Found" response, at least to my understanding. Furthermore, all of the new default behavior remains customizable by the user.

Accepting this PR in its current form would essentially mean that the URLPattern would be the only factor determining whether a Route can handle the request or not.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.34%. Comparing base (c40f593) to head (6f1d3e6).

Additional details and impacted files

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  Coverage   96.33%   96.34%           
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  Files         547      547           
  Lines       41667    41681   +14     
  Branches     6314     6316    +2     
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+ Hits        40140    40157   +17     
+ Misses       1484     1482    -2     
+ Partials       43       42    -1     

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