Fix readout of netpbm images containing empty lines (such as those produced by GIMP)

See merge request !43

Fix c++ exception throw

See merge request !42

Resolve "GIF loading seems to be completely broken"

Closes #26

See merge request !24

Merge branch '32-versions-of-image-libraries-are-evaluated-by-hand-and-given-as-parameters-on-the-compiler-command-line' into 'master'

Resolve "versions of image libraries are evaluated by hand and given as parameters on the compiler command line"

Closes #32

See merge request !41

Matplotlib is not a build time dependency

See merge request !40

Relax matplotlib requirement

Closes #31

See merge request !39

It's only used in one utility function therefore the import
has been moved within the function and the requirement moved to
run_constrained.

Fixes #31

Add tests to detect the problem reported on this issue

Closes #30

See merge request !36