library/fatter_sparse_bitset.m:
Add this version of fat_sparse_bitset.m, which stores *two* words
worth of bits in each cell, not one. This word would otherwise be unused,
because the Boehm-Demers-Weiser allocator rounds up requests for three
word cells to four.
library/MODULES_DOC:
library/library.m:
Add the new module to the list of library modules.
library/fat_sparse_bitset.m:
library/sparse_bitset.m:
library/tree_bitset.m:
Update the documentation of all these other bitset modules. Copy
the same basic introduction to all the relevant modules. Add documentation
of the differences to tree_bitset.m and fatter_sparse_bitset.m, with
a pointer in fat_sparse_bitset.m to fatter_sparse_bitset.m.
library/test_bitset.m:
Test the new module as well as the others.
tests/hard_coded/speedtest_bitset.m:
Extend the benchmarking of list_to_set operations to the new module.
To allow the benchmarking to be tough enough to be informative, comment
out the benchmarking of the old_list_to_set operations.
