Allow setting and scaning interface{} values.

[vmihailenco]

Should make client a little bit more convenient to use. @dim?

Fixes #121. Before

BenchmarkRedisBytes    10000        120101 ns/op       52809 B/op         16 allocs/op
BenchmarkRedisSet      30000         45606 ns/op       10666 B/op          7 allocs/op

After

BenchmarkRedisBytes    10000        108434 ns/op       32022 B/op         21 allocs/op
BenchmarkRedisSet      30000         46389 ns/op       10762 B/op         10 allocs/op

[vmihailenco]

@dim ping :) I am not worried about the code, but more about approach in general.

[dim]

I would probably define a type Encodable interface { EncodeRedis() (string, error) } and return an error on default

[dim]

Please see #121 too

[vmihailenco]

@dim PTAL

Before

BenchmarkRedisSet      30000         44599 ns/op       10666 B/op          7 allocs/op
BenchmarkRedisSetBytes     30000         51482 ns/op       21163 B/op          8 allocs/op
BenchmarkAppendArgs 10000000           155 ns/op           0 B/op          0 allocs/op

After

BenchmarkRedisSet      30000         45297 ns/op       10746 B/op         10 allocs/op
BenchmarkRedisSetBytes     30000         45215 ns/op       10762 B/op         10 allocs/op
BenchmarkAppendArgs 10000000           223 ns/op           0 B/op          0 allocs/op

[vmihailenco]

@dim ping

[dim]

Hey, sorry, I'm away until next week, but results look good

[vmihailenco]

Np, this can wait.

[vmihailenco]

@dim last time ping :)

[dim]

Sorry, traveling (again), will review this week, promise, but should be OK to merge in the meantime anyway