Redis-namespace

- Fix: (Security) don't proxy `exec` through `method_missing`
- Fix 62: Don't try to remove namespace from `Redis::Future`
- Fix 61: Support `multi` with no block
- Feature 58: Support `echo`, `exec`, `strlen` commands

Features:
- Added commands: `multi`, `pipelined`, `mapped_mset`, and `mapped_msetnx`
- Added temporary namespaces that last for the duration of a block
- Unknown commands now warn
- Added `mapped_mset` command

Also lots of bug fixes.

Features:
- make redis connection accessible as a reader

Features:
- added mapped_hmset (hectcastro, 32)
- added append,brpoplpush,getbit,getrange,linsert,lpushx,rpushx,setbit,setrange (yaauie, 33)
- use Redis.current as default connection (cldwalker, 29)
- support for redis 3.0.0 (czarneckid, 39)