Implement decoding and encoding of boolean values.

[jchv]

It would appear that neither the encoder nor decoder attempt to handle booleans.

Proposed behavior:

CBool   bool                    // would be decoded as an 8-bit boolean, like C.
1Bit    bool `struct:"uint8:1"` // single bit boolean
1BitAlt bool `struct:"bool:1"`  // another single bit boolean
32Bit   bool `struct:"uint32"`  // 32-bit integer boolean

• Zero is translated into false.
• Anything else is translated into true.
• In encoding, true is translated to 1.
• If additional behaviors are needed, they should be implemented as flags most likely.