Convenience methods for adding routes

[bnkamalesh]

Is your feature request related to a problem? Please describe.

Adding routes currently requires the developer to prepare a single list of *Route with all the routes defined in one go. This can be split up and made easier for the developer

Describe the solution you'd like

We can add convenience method for each type of HTTP method supported by webgo (). e.g.

router.Add(*Route)
router.Get("URI",[]Handlers{}, opts...)
router.Head("URI",[]Handlers{}, opts...)
router.Post("URI",[]Handlers{}, opts...)
router.Put("URI",[]Handlers{}, opts...)
router.Patch("URI",[]Handlers{}, opts...)
router.Delete("URI",[]Handlers{}, opts...)
router.Option("URI",[]Handlers{},opts...)

Each method should keep updating routes of the router, for the respective HTTP method.

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Additional context
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