* Modernize bitfield.cc: Grouped member functions into the struct; C++ construction
* Modernize bitfield.cc: Naming style similar to qt/ C++ source
* Modernize bitfield.cc: Bitfield test updated to new API
* Modernize bitfield.cc: Renames for private functions
* Modernize bitfield.cc: Formatting
* Modernize bitfield.cc: Remove struct in 'struct Bitfield' and update commented code too
Co-authored-by: Charles Kerr <charles@charleskerr.com>