Add bitwise AND, OR, and XOR operations

[maxijb]

Summary

• Add mutating and, or, and xor operations for equal-length BitSets.
• Keep the ES5 distribution in sync.
• Document the new methods and cover them with tests.

Testing

• ./node_modules/.bin/jest spec/bitset.test.js --runInBand --config='{"transform":{}}'
• Direct Node.js checks against lib/BitSet.js and lib/BitSetES5.js

Note

The repository has no main branch, so this PR targets its default branch, master.