Dep compatibility

[kollektiv]

Fixes: #1148, #1143

Currently if you try to use dep with go-redis v7, dep will place the files in ./vendor/github.com/go-redis/redis, and then error because the imports, github.com/go-redis/redis/v7, are mismatched with file locations. Dep minimal module awareness issue: golang/dep#1962

Go files have been moved to the top-level into the "v7" subdirectory. This makes it possible to use go-redis v7 with the dep dependency manager, and still compatible with go modules. dep places files on disk at "./github.com/go-redis/redis/v7".

The forward.go file is generated using goforward (https://go-review.googlesource.com/c/tools/+/137076/) to add aliases that point to github.com/go-redis/redis to github.com/go-redis/redis/v7. The goforward tool is mentioned in this section https://github.com/golang/go/wiki/Modules#releasing-modules-v2-or-higher

[vmihailenco]

Sorry, but this is considerable amount of work and demand is not high. I've migrated all projects to go mod and don't regret it - in long term that is the best and simplest thing to do.