Fix "loss of data ..." error in Decimal

Using default precision for Decimal (28) we get an error is the string represents a number with higher precision.

Error: Loss of data on string conversion in ... on line 1

So we need to truncate the string before instantiating the Decimal object.

Operation: multiply

• Add multiplication
• Basic CI with https://travis-ci.org. WIP.

Operations: pow and add

Basic complex operations needed for Mandelbrot formula:

• pow
• add