Create sqrt.go

[kempeng]

Implementation of Square Root for decimals

[ldcicconi]

you need to consider the case that 0 < d < 1 .

Something like

	if d.GreaterThanOrEqual(decimal.One) {
		lo = decimal.Zero
		hi = d
	} else if d.Equal(decimal.One) {
		return one
	} else if d.LessThan(decimal.Zero) {
		return decimal.NewFromFloat(-1), false // this is an error here, cant take sqrt of neg w/o imaginaries
	} else if d.Equal(decimal.Zero) {
		return decimal.Zero
	} else {
		// d is between 0 and 1. Therefore, 0 < d < Sqrt(d) < 1.
		lo = d
		hi = one
	}

[mwoss]

Improved implementation, with edge case handling in #130. I'm closing this PR.