Improvement to mode algorithm

[nchinling]

Issue description:
The current implementation to find the mode returns only one mode value. If there are more than one modes, it prints only the first mode value.

It is possible to have multiple modes given a list of numbers:
E.g.
{2, 2, 17, 2, 16 16, 15, 16}
The modes are 2 and 16.

I would like to work on this. Can you assign this issue to me?

[stale]

This issue has been automatically marked as stale because it has not had recent activity. The issue will be unassigned if no further activity occurs. Thank you for your contributions.

[sharara6]

i will be working on this can you assign me please ?

[sharara6]

Dear @iluwatar may you check my PR?