Updated Bitfield implementation to use RangeSetBlaze instead of BTreeSet

[louisgregg]

This PR addresses issue #5

• Using RangeSetBlaze instead of a BTreeSet in our Bitfield implementation should allow for more space efficient storage of hypercore chunk indices.
• This may also provide faster inserts/lookups under some circumstances.
• Added an additional unit test to check that set_range on DumbBitField behaves as intended when setting values to false.
• Introduces dependancy on external range_set_blaze crate, where previously we only needed std::collections for the BTreeSet.