source/fitz/memento.c: Added verbose control.
source/fitz/memento.c: Added verbose control.

Omit detailed diagnostics if environmental variable MEMENTO_VERBOSE is '0';
useful when there are many leaked blocks, provides similar runtime equivalent
to build-time MEMENTO_DETAILS. Also controllable with new Memento_setVerbose()
function.

For clarity, explicitly show zero leaked blocks if no leaks.

showInfo(): show "Known Leak" like showBlock().

ArtifexSoftware/mupdf,ArtifexSoftware/mupdf,ArtifexSoftware/mupdf,ArtifexSoftware/mupdf,ArtifexSoftware/mupdf,ArtifexSoftware/mupdf,ArtifexSoftware/mupdf,ArtifexSoftware/mupdf