Recommend to split remote implements to multi repos

[wyxloading]

Now package remote stick in the viper repo, leave us many dependencies.

How about spliting those remote implements to separate repos, like viper-consul, viper-etcd. Then we could choose what we actually need.
Also contributors can write different remote implementations of their own, which should not fire as a mr to viper.

[sagikazarmark]

Eventually that would be nice, but for v1 we can't really remove those dependencies without breaking BC.

Since the package now uses go modules, we could make the remote package a separate module.

[wyxloading]

see #772