Returns a trendline (line), support or resistance

		Parameters:
			date0 : string
				Trendline starting date			
			date1 :  string
				Trendline end date
			on : string
				Indicate the data series in which the 
				trendline should be based.
					'close'
					'high'
					'low'
					'open'			
			kind : string
				Defines de kind of trendline
					'trend'
					'resistance'
					'support'			
			mode : string
				Defines how the support/resistance will 
				be drawn
					'starttoened' : (x0,x1)
					'fromstart' : (x0,date0)
					'toend'	: (date0,x1)
			text : string
				If passed, then an annotation will be added 
				to the trendline (at mid point)
			from_strfmt : string
				Defines the date formating in which 
				date0 and date1 are stated. 
				default: '%d%b%y'				
			to_strfmt : string
				Defines the date formatting 
				to which it should be converted. 
				This should match the same format as the timeseries index. 
				default : '%Y-%m-%d'

def _get_trendline(self,date0=None,date1=None,on=None,kind='trend',to_strfmt='%Y-%m-%d',from_strfmt='%d%b%y',**kwargs):
		"""
		Returns a trendline (line), support or resistance

		Parameters:
			date0 : string
				Trendline starting date			
			date1 :  string
				Trendline end date
			on : string
				Indicate the data series in which the 
				trendline should be based.
					'close'
					'high'
					'low'
					'open'			
			kind : string
				Defines de kind of trendline
					'trend'
					'resistance'
					'support'			
			mode : string
				Defines how the support/resistance will 
				be drawn
					'starttoened' : (x0,x1)
					'fromstart' : (x0,date0)
					'toend'	: (date0,x1)
			text : string
				If passed, then an annotation will be added 
				to the trendline (at mid point)
			from_strfmt : string
				Defines the date formating in which 
				date0 and date1 are stated. 
				default: '%d%b%y'				
			to_strfmt : string
				Defines the date formatting 
				to which it should be converted. 
				This should match the same format as the timeseries index. 
				default : '%Y-%m-%d'		
		"""
		ann_values=copy.deepcopy(get_annotation_kwargs())
		ann_values.extend(['x','y'])
		ann_kwargs=utils.check_kwargs(kwargs,ann_values,{},clean_origin=True)
		def position(d0,d1):
			return d0+(d1-d0)/2

		date0=kwargs.pop('date',date0)    
		date0=date_tools.stringToString(date0,from_strfmt,to_strfmt) if '-' not in date0 else date0
		
		if kind=='trend':
			date1=date_tools.stringToString(date1,from_strfmt,to_strfmt) if '-' not in date1 else date1
			on='close' if not on else on
			df=pd.DataFrame(self.df[self._d[on]])
			y0=kwargs.get('y0',df.ix[date0].values[0])
			y1=kwargs.get('y1',df.ix[date1].values[0])
			
		
		if kind in ('support','resistance'):
			mode=kwargs.pop('mode','starttoend')
			if not on:
				on='low' if kind=='support' else 'high'
			df=pd.DataFrame(self.df[self._d[on]])
			y0=kwargs.get('y0',df.ix[date0].values[0])
			y1=kwargs.get('y1',y0)
			if mode=='starttoend':
				date0=df.index[0]
				date1=df.index[-1]
			elif mode=='toend':
				date1=df.index[-1]
			elif mode=='fromstart':
				date1=date0
				date0=df.index[0]

		if isinstance(date0,pd.Timestamp):
			date0=date_tools.dateToString(date0,to_strfmt)
		if isinstance(date1,pd.Timestamp):
			date1=date_tools.dateToString(date1,to_strfmt)
		d={'x0':date0,'x1':date1,'y0':y0,'y1':y1}
		d.update(**kwargs)
		shape=tools.get_shape(**d)        

		
		if ann_kwargs.get('text',False):
			ann_kwargs['x']=ann_kwargs.get('x',date_tools.dateToString(position(date_tools.stringToDate(date0,to_strfmt),date_tools.stringToDate(date1,to_strfmt)),to_strfmt))
			ann_kwargs['y']=ann_kwargs.get('y',position(shape['y0'],shape['y1']))
		else:
			ann_kwargs={}
		return {'shape':shape,'annotation':ann_kwargs}