Doubles: reasons for disallowing exponential form

The specification indicates, for doubles:

> Exponential format is invalid.

However, this means that very large and very small values are now very verbose on the wire; additionally, many frameworks make *not* using E format challenging. This is also contrary to previous redis handling, which allows E formats, for example in the `INCRBYFLOAT` documentation there exists the sample:

``` txt
INCRBYFLOAT mykey 2.0e2
```

For example, IEEE754's max/min values would be over 300 bytes, to transmit a theoretically 8 byte payload.

I'd like to challenge whether this is a good idea, preferring to allow exponential form when appropriate. It is also notable that some platforms make it actively hard to *not* use E form.