Column alignment for large numbers

[dtolnay]

The alignment is broken when numbers get large.

Echidnatron% time cargo llvm-lines
   Compiling tpchlike v0.1.0 (file:///Users/mcsherry/Projects/differential-dataflow/tpchlike)
    Finished dev [unoptimized + debuginfo] target(s) in 352.27 secs
1332608 2031  <core::slice::Iter<'a, T>>::search_while
 440031 4621  <core::option::Option<T>>::map
 419929 21396  core::ptr::drop_in_place
 347867  745  alloc::slice::merge_sort
 306676 1394  <alloc::raw_vec::RawVec<T, A>>::double
 219402  745  alloc::slice::insert_head
 208600  745  alloc::slice::merge

[dtolnay]

Fixed by #22.