use http.FileSystem interface and support 3rd party implementation

[yankeguo]

Golang provides a interface http.FileSystem and and a method http.Dir to abstract static file serving.

Iis it possible to refine static middleware with support of http.FileSystem, thus 3rd party http.FileSystem implementation (embedded file system) can integrate with Echo ?

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[pafuent]

Just reopening to close it as fixed

[pafuent]

Fixed by #1797