v3.1.0

features:

• time and date-time formats now understand leap-second
• new formats duration, uuid are added
• jv command now supports optional -draft flag

changes:

• errors now implement GoStringer interface
  the Error method now just returns single line
• format ipv4 now rejects leading zeroes
• updated JSON-Schema-Test-Suite to latest

bugfixes:

• $ref should be resolved against current uribase
  currently it is always resolved against root uri base