0.8.0

What's Changed

• Change conversion of NTP64 and Timestamp to/from String (#16).
  For both NTP64 and Timestamp types the default formatting used by Display trait (and thus by ToString trait) changed. RFC3339 format was used to represent the NTP64 type, which was loosing precision and was not bijective with FromStr trait (see #15). Now unsigned integer decimal representation is used.
  The to_string_rfc3339_lossy() and parse_rfc3339() methods have been added for explicit conversion to RFC3339 format.

Full Changelog: 0.7.0...0.8.0