Now validating incoming requests

Most requests now must follow the "standard" structure that resembles
the following:

{
  'line_num': NUMBER,
  'column_num': NUMBER,
  'filepath': PATH_TO_FILE,
  'file_data': {
    PATH_TO_FILE: {
      'filetypes': [ FILETYPE ],
      'contents': CONTENTS
    }
  }
}

Otherwise the server rejects the request.

Fixes #31.