* [WIP] added UserOperation enum, added IndexWriter.run, and added MultiStamp
* removed MultiStamp in favor of std::ops::Range
* changed IndexWriter::run to return u64, Stamper::stamps to return a Range, added tests, and added docs
* changed delete_cursor skipping to use first operation's opstamp vice last. change index_writer test to use 1 thread
* added test for order batch of operations
* added a test comment
* Moving lock to directory/
* added fs2
* doc
* Using fs2 for locking
* Added unit test
* Fixed error message related unit test
* Fixing location of import
* Closes 471
Removing writing_segments in the segment manager as it is now useless.
Removing the target merged segment id as it is useless as well.
* RAII for tracking which segment is in merge.
Closes#471
* fmt
* Using Inventory::default().
* add unit test
* improved test
* added SegmentManager#remove_empty_segments
* update old tests for new behaviour
* cleaner filter for empty segments
* PR adjustments
* rename x in closures
* simplify assert_eq!(vec.len(), 0)
* wait_merging_threads
* acquire searchers
* add comments to test
* rebased on latest master
* harden test
* fix merger#test_merge_multivalued_int_fields_all_deleted test
* Using unrolled u32 VInt and caching Vec s
* cargo fmt
* Exposing a io::Write in the Expull thing
* expull as a writer. clippy + format
* inline the first block
* simplified -if let Some-
* vint reader iterator
* blop
* Using unrolled u32 VInt and caching Vec s
* cargo fmt
* Exposing a io::Write in the Expull thing
* expull as a writer. clippy + format
* inline the first block
* simplified -if let Some-
* vint reader iterator
