text: Title: one hot encoder has the option to automatically drop the second binary variable for binary categorical variables
  Body: We need to add one parameter to the init method of the one hot encoder, called for example automate_drop_last_binary that when True, will automatically return 1 binary variable if the original variable was binary.
  
  Details:
  - automate_drop_last_binary should default to False not to break backwards compatibility
  - automate_drop_last_binary would only work for binary variables
  - automate_drop_last_binary would only work if drop_last=False
  
  When automate_drop_last_binary=True, binary variables would result in the addition of just one dummy instead of 1. So for the variable colour, with categories black and white, instead of returning the binary colour_black and colour_white, which are redundant, it would only return colour_black
  
  In addition, we should add an attribute in the fit method called for example binary_variables_ where the transformer returns a list with the names of the binary variables.
  
  To finish of this PR, we need to add 1-2 tests to make sure that the behaviour is the expected