Remove Dependencies and Duplicated Code

[kyleyost19]

Issue #, if available:
The last comment on #22 is relevant

Description of changes:

• Remove vendor folder as it should not be included for libraries without a package main
• Remove all "adapters" as they are not needed. Each router that is supported implements http.Handler, so there is no need to couple this project with those routers. Let the users of this library choose what router and version they want to use.
• Simply renamed the httpadapter package to proxy and everything else is left in tact. Obviously this is a breaking change, but I left all the other code as unchanged as possible

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.