treez

A collection of useful data structures

implemented:

- segment tree
  + usage:
  ```let mut segments = vec![];
     for i in 0..10 {
         let n = (i*5, 5*i+5, i); //(left_bound,right_bound,segment_id); inclusive bounds
     segments.push( n );
 }
 let t : treez::seg::TreeSeg = treez::seg::TreeSeg::init( segments.as_slice() );
 
 let check: HashSet<_> = [ 2, 3, 4 ].iter().cloned().collect();
 let query_segs: HashSet<_> = t.get_segs_from_bound( (15,20) ).iter().cloned().collect();
 println!( "query segs: {:?}", query_segs );
 assert!( check.intersection(&query_segs).count() == check.len() );```