add update and update! methods for fast batch updates
Merge branch 'master' of github.com:propublica/daybreak
add comments
fix compact and new_records

- compact check for concurrent compactification was invalid
- compactsize can be checked outside of exclusive
- new_records: loop is only necessary if we are not already exclusively locked
add flock method
rename exclusive to with_flock
add more text about benchmarks

[ci skip]
Merge branch 'master' into gh-pages
Merge branch 'gh-pages' of github.com:propublica/daybreak into gh-pages