Data.List: Add find_index and find_indices functions
Data.List: Add find_last_index function
Data.List: Fix code format
Data.List: Fix comments
Data.List: Fix an error caused if a:start is over the range
Data.List: Fix an error with negative a:start
Merge pull request #200 from cohama/add-find_index

Data.List: Add find_index and find_indices functions