Added Dataset class

When the class is initiated, basic descriptive statisics of the dataset is calculated

Calculates the mean, median, mode, population SD, sample SD, population variance, sample variance, n, min n, max n

self.histogram(_bin, title, x_label, y_label):
	Plots a histogram of the data with 'title' title, 'x_label' label for x and 'y_label' label for y.
	Max Y is 1.1 * self.max (maximum value of dataset)