docs: 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)