Update type typo for Header handler (labstack#868)

The example for ServerHeader middleware is trying to set a `Echo/3.0` header,
but the response out put has a Echo/2.0 header, may confuse people.

issue: fixed labstack#755 (labstack#758)

Signed-off-by: Vishal Rana <[email protected]>

updated docs

Signed-off-by: Vishal Rana <[email protected]>

fixed labstack#729

Signed-off-by: Vishal Rana <[email protected]>

updated migration guide

Signed-off-by: Vishal Rana <[email protected]>

updated docs, readme and benchmark tests (labstack#718)

* updated docs, readme and benchmark tests

Signed-off-by: Vishal Rana <[email protected]>

* fixed labstack#719

Signed-off-by: Vishal Rana <[email protected]>

updated docs

Signed-off-by: Vishal Rana <[email protected]>

updated docs

Signed-off-by: Vishal Rana <[email protected]>

backport fix for labstack#623 from v3 (labstack#709)

changes README's hello-world example for v3 (labstack#698)

* [doc] adding graceful documentation and example.

* adding myself to the maintainers list and minor comment formatting change

* [doc] updating code on the guides/context.md and guides/cookies.md to use v3 code.

* [doc] updating error-handling and request to v3 codebase

* [doc] updating templates documentation

* [doc] cleaning hello-world documentation for v3

* [content] adding website index content based on labstack#667