Add Bollinger Bands (BOLL) study to QuantFigure.studies

		Parameters:
			periods : int or list(int)
				Number of periods
			boll_std : int
				Number of standard deviations for
				the bollinger upper and lower bands
			fill : boolean
				If True, then the innner area of the 
				bands will filled
			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
			fillcolor : string
				Color to be used for the fill color.
				Example:
					'rgba(62, 111, 176, .4)'
			All formatting values available on iplot()

def add_bollinger_bands(self,periods=20,boll_std=2,fill=True,column=None,name='',
						   str='{name}({column},{period})',**kwargs):
		"""
		Add Bollinger Bands (BOLL) study to QuantFigure.studies

		Parameters:
			periods : int or list(int)
				Number of periods
			boll_std : int
				Number of standard deviations for
				the bollinger upper and lower bands
			fill : boolean
				If True, then the innner area of the 
				bands will filled
			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
			fillcolor : string
				Color to be used for the fill color.
				Example:
					'rgba(62, 111, 176, .4)'
			All formatting values available on iplot()
		"""
		if not column:
			column=self._d['close']
		study={'kind':'boll',
			   'name':name,
			   'params':{'periods':periods,'boll_std':boll_std,'column':column,
						'str':str},
			  'display':utils.merge_dict({'legendgroup':True,'fill':fill},kwargs)}
		self._add_study(study)