fixed dead link.
foundation::HashTable now requires the table size to be a power of two.
fixed regression: total rendering time was no longer written to the log panel in appleseed.studio.

regression introduced in fedd9029aaa40cdf5c13cdf118f0c15cdf2e6e31 ("bug fix: the rendering time displayed in appleseed.studio's status bar was sometimes incorrect when rendering failed.").

also cleaned up the foundation::Stopwatch API.
updated test suite reference images.
the microfacet BRDF model is now considered glossy rather than diffuse.