v0.15.0

• build
  • add max to make -j
  • improve path for Windows to use currently configured GOPATH
• core
  • Add Mat.DataPtr methods for direct access to OpenCV data
  • Avoid extra copy in Mat.ToBytes + code review feedback
• dnn
  • add test coverage for ParseNetBackend and ParseNetTarget
  • complete test coverage
• docs
  • minor cleanup of language for install
  • use chdir instead of cd in Windows instructions
• examples
  • add 'hello, video' example to repo
  • add HoughLinesP example
  • correct message on device close to match actual event
  • small change in display message for when file is input source
  • use DrawContours in motion detect example
• imgproc
  • Add MinAreaRect() function
• test
  • filling test coverage gaps
• videoio
  • add test coverage for OpenVideoCapture