Implemented power function

[Ares358]

Resolves Issue #128

Description

Implemented a power function where power(x,n) returns x^n.

How to run

Update the values of x, y in the driver code or take input from the user.

Checklist

• [x] Code compiles correctly.
• [x] Changes are tested properly.
• [ ] Added the README / documentation, if necessary.
• [x] Followed the Contributing guidelines.
• [x] Resolved merge conflicts, if any.

[Ares358]

@amukh18 requesting review

[amukh18]

LGTM. @krithikvaidya could you please merge this?