This class provides a constant-size bitmap that can be used as almost a
drop-in replacement for bitmaps stored in integer types.  The
implementation is entirely within the header file and uses recursive
templated operations to support effective optimisation and usage in
constexpr expressions.

This initial implementation hardcodes the choice of uint64_t elements
for storage and initialisation, but this could instead be specified via
a second template parameter.

gcc/ChangeLog:

	* bbitmap.h: New file.