add zeronormals test tool
stl filter which resets face normals to 0 0 0
Define our own face_max limit based on uint32_max
better clarity about meaning of that constant when tested against facecount
Tweak name of face normal tweaking functions, minor reorganization of header
trixResetNormals is now trixZeroNormals; trixRecalculateNormals is now trixUpdateNormals
Draft documentation in header (and removed generic error result type)