add insert_sort

http://en.wikipedia.org/wiki/Insertion_sort
add gitignore
add bubble_sort

http://en.wikipedia.org/wiki/Bubble_sort
use `downto` and `upto` instead of range.to_a

http://stackoverflow.com/questions/2070574/is-there-a-reason-that-we-cannot-iterate-on-reverse-range-in-ruby