Fix encoding for float64 and generate conversion for Timestamp

Fix encoding for float64 and generate conversion for Timestamp

- fixes encoding/decoding of float64 - uses little endian (contrary to all other types)
- generates helper methods for vpe_types.Timestamp type
- adds usage code to simple-client and binapi-types examples

Change-Id: I2e83eee0629eb67964049406c50c7ee0a692ccaf
Signed-off-by: Ondrej Fabry <ofabry@cisco.com>