extends Material::parse() to support bitmap textures
material.cc: multiple improvement in procedural textures, but still a bug

Lambdas generated by Material::makeProceduralFunctor() are almost always
called with (x,y) = (0,0). This shouldn't be possible, since these lambdas are
called through Shape::computeColorFromTexture(), which is supposed to cache
its own results in an std::unordered_map.
report.tex: fill the 'textures' section
report.tex: fix typos