Fix #int_to_decimal to correctly pad 0s
Add User#splits_with
Move #int_to_decimal to new module Utilities
Require Utilities
Add #decimal_to_int
Use Utilities helper methods
Change methods to be on module
Utilities doesn't need to be explicitly required
Change . to ::
Sort user_ids before building map
Fix incorrect rounding
Change #splits_with to include bills
Add BillSplit::sum_for_user
Add check for empty splits
Formatting
Setup show_other view
Basic other user view
Configure #index and #show views
Remove Bill#index view
Add description presence validation