Version bumps

Correct location of Dockerfile

Minimum version of libvips now 7.40.0 lovell#74

Prevent auto-rotate fail for libmagick formats lovell#117

Version bumps ahead of v0.7.1

Code lint of new features

Improve Stream error handling lovell#88

Add support for C++11 on Mac

Small doc improvements ahead of v0.6.0

Use tile cache for interlace output

Doubles performance of Adam7 interlaced PNG output