Merge pull request #299 from est77/OSL_merge

OSL merge 7
small code tweaks and cosmetic fixes.
Update README.md
fixed generation of Doxygen documentation.

the 'dot' tool could not be invoked by Doxygen if it wasn't in the path.
Update README.md
Update README.md
Update README.md
Update README.md
Update README.md
Update README.md
command line tools now understand the --message-verbosity <level> command line argument.

level can be: debug, info, warning, error, fatal.
added syntax for --configuration <name> command line argument.
missing positional arguments is now a fatal error; simplified the code accordingly.
Adding shader class, extending containers to handle OSL related classes, fixed assembly's on_frame_begin.