order initializers by the members' order in the class declaration

(clang's -Wreorder)
make forward decls of structs/classes match keyword of full decl

(clang's -Wmismatched-tags)
removed unused members

(clang's -Wunused, -Wunused-private-field)
force-inherit virtual base class methods with subclass overloads

Also, disambiguate some of the ambiguous calls this causes.

(clang's -Woverloaded-virtual)
use std::abs instead of abs on floating-point values

(clang's -Wabsolute-value)
add missing newlines to the ends of files