Add tags, todo, *.bench, *.svg and bench_output to .gitignore
Add test/bench.sh script. bench.sh runs the `bench` command on each
test/long*txt file with range 3:5 and saves the output to a file for
comparing performance across file sizes.
Inline printing in get_choice_slice
Change BufWriter<..stdout..> to BufWriter<T>
Add MockStdout for testing printing
Add more reverse range tests
Simplify word finding with a more uniform bounds check.
Add Makefile for generating flamegraphs
Redefine Choice struct as a start and end integer
Improve algorithm for finding words to print
Settle exclusivity at Config construction time
Add tests for nonexistant field_seps
Add regression test for preceding separator
Use handle.write instead of write! macro for tremendous speed up
