Extend ROUND() and FLOOR() to include number of decimal places to round up/down

[spena]

The functions ROUND() and FLOOR() currently accepts one single argument which will be rounded up or down to an integer.

We should extend these functions to accept a second argument that specifies the number of decimal places to round the value. This will be useful when users want to convert DECIMAL types (See #842) and a default rounding happens during conversion to a smaller scale.

Syntax to support:

• ROUND(n [, d]) where n is the value to round up, and d is a number indicating up to how many decimal places In will be rounded.
  i.e.

ROUND(3.6456, 3) = 3.646
ROUND(3.6456, 2) = 3.65
ROUND(3.6456) = 4

• FLOOR(n [, d]) where n is the value to round down, and d a number indicating the number of places after the decimal to which to round downward.
  i.e

FLOOR(3.6456, 3) = 3.645
FLOOR(3.6456, 2) = 3.64
FLOOR(3.6456) = 3

[agavra]

This was fixed by #3404 - thanks @purplefox !