text: Title: Add docstrings to everything 
  Body: You can do:
  
  `pip install pydocstyle`
  and then run this script while in the `pyt` directory
  
  ```python
  import os
  import re
  import subprocess
  import sys
  
  
  os.chdir(os.path.join('pyt'))
  
  try:
      docstyle = subprocess.run(["pydocstyle", "--ignore=D105,D203,D212,D213"],
                                stderr=subprocess.PIPE, universal_newlines=True)
  except FileNotFoundError:
      print('Error: Install pydocstyle with pip for python 3.'
            ' Something like: "sudo python -m pip install pydocstyle"')
      sys.exit()
  
  lines = re.split('\n', docstyle.stderr)
  
  errors = zip(lines[0::2], lines[1::2])
  
  errors = [x + "\n\t" + y for x, y in errors]
  
  errors = [error for error in errors if 'visit_' not in error]
  
  for error in errors:
      print(error + '\n')
  
  print("Total errors: {}".format(len(errors)))
  ```
  
  It'll spit out which functions don't have docstrings or complain about something non-[PEP 257](https://www.python.org/dev/peps/pep-0257/) compliant.
  
  This is a great way to learn the codebase, and everyone will love you for it.
  
  The [imports code for example](https://github.com/python-security/pyt/blob/master/pyt/stmt_visitor.py#L716-L1013) does not have docstrings, for example.
  
  For an example of great docstrings, see the [user-defined function calls code](https://github.com/python-security/pyt/blob/master/pyt/expr_visitor.py#L187-L495).
  
  Afterwards, we can maybe add [it as a pre-commit hook](https://github.com/chewse/pre-commit-mirrors-pydocstyle).