Add features from libvips 7.40+

Load TIFF from Buffer/Stream

Interlaced PNG output no longer needs tilecache

Option to disable PNG adaptive row filtering
Shrink less, affine more, maintain performance #75

Affects interpolators with 4x4+ window size

e.g. Bicubic, LBB, Nohalo

Introduces blur before large affine

to improve large PNG reductions
Control level of sharpening via radius/flat/jagged #108
Ensure leak check tests child processes
Add 'fast' blur and Gaussian blur feature #108
Disable libvips cache for unit tests

Aids memory leak detection
Less C, more C++ e.g. namespace, enum class

Improve image reference handling
Add bounds checks on blur/sharpen parameters #108
Additional blur radii tests #108
Ubuntu 14 now compiles 7.40.x from source

as packaged version is the outdated 7.38.x

Added support for Ubuntu 15 and Mint 17.1
Minimum version of libvips now 7.40.0 #74