Enabled G++ warnings.
Removed many warnings from LuaValue.cpp.

Most of them are "dereferencing type-punned pointer will break
strict-aliasing rules [-Wstrict-aliasing]". My changes to the code
don't do really much, but they do enough to suppress the warning. As
far as I can tell, there is no actual problem in that code.
Got rid of all the remaining warnings.

Now, these were all "extra ';'" warnings -- caused by, er, extra ';'s
after macro calls.
Updated the project homepage in the documentation.
Bumped version in Doxyfile to the current one (0.5.5).
Trying to fix the mess I made during the latest pull request.