Fixed the column looping over the width instead of height
Removed an unused parameter to the column calculation closure
Synchronize access to the completion accumulator var
Replaced panic()'s with log.Fatalf()
Simplified opening and creating the output file
Merge branch 'master' of https://github.com/ghthor/bbmandelbrot.go into ghthor-master

Conflicts:
	bbmandelbrot.go