0.0.7 release
Fixes the doctests -- they weren't running in latest rustc
Merge pull request #43 from cgaebel/fix-tests

Fixes the doctests -- they weren't running in latest rustc
add `compare` module with comparators
parameterize `IntervalHeap` with a comparator
implement `Default` for comparators
rename methods

- s/with_capacity_cmp/with_capacity_and_cmp/
- s/from_vec_cmp/from_vec_and_cmp/
s/inteval_heap_push/interval_heap_push/
use `Default` in `IntervalHeap` constructors
remove type parameters from `Natural`
update `IntervalHeap` docs
re-parameterize `Natural`

this helps drive type inference
re-order some items
consolidate whitespace
re-order type parameters
add `Extract` comparator
flesh out docs