Previously, when cmake was missing, the build dir would
be created anyway, and subsequent attempts (even with cmake)
would fail, because cmake would not be run.
Depending on build/CMakeFiles is more robust -- this
won't be created unless cmake is run.
Partially addresses #85.
It simplifies the build if python and the cmark library aren't
needed to build the man page.
The top level Makefile has a rule to regenerate this when src/cmark.h
changes.
Updated Makefile.nmake for recent changes.
Added case folding data file to archive, since otherwise make fails.
This tests the dynamic library when run without a second argument.
The code makes use of an amended version of the normalization
method from karlcow/markdown-testsuite.
Closes#161.
