Add Simple Moving Average (SMA) study to QuantFigure.studies

		Parameters:
			periods : int or list(int)
				Number of periods
			column :string
				Defines the data column name that contains the 
				data over which the study will be applied. 
				Default: 'close'
			name : string
				Name given to the study
			str : string
				Label factory for studies
				The following wildcards can be used:
					{name} : Name of the column
					{study} : Name of the study
					{period} : Period used
				Examples:
					'study: {study} - period: {period}'
		kwargs: 
			legendgroup : bool
				If true, all legend items are grouped into a 
				single one
			All formatting values available on iplot()

def add_sma(self,periods=20,column=None,name='',
					str=None,**kwargs):
		"""
		Add Simple Moving Average (SMA) study to QuantFigure.studies

		Parameters:
			periods : int or list(int)
				Number of periods
			column :string
				Defines the data column name that contains the 
				data over which the study will be applied. 
				Default: 'close'
			name : string
				Name given to the study
			str : string
				Label factory for studies
				The following wildcards can be used:
					{name} : Name of the column
					{study} : Name of the study
					{period} : Period used
				Examples:
					'study: {study} - period: {period}'
		kwargs: 
			legendgroup : bool
				If true, all legend items are grouped into a 
				single one
			All formatting values available on iplot()
		"""
		if not column:
			column=self._d['close']
		study={'kind':'sma',
			   'name':name,
			   'params':{'periods':periods,'column':column,
						 'str':str},
			  'display':utils.merge_dict({'legendgroup':False},kwargs)}
		self._add_study(study)