v0.2.4

[atom-tr]

• Add docstring for function
• Deploy rtd site

Enhancements

• Add the option 'pixel_position', with the default set to 'top', without appending it to the end of the HTML body.  
  > TODO 6: Document caveats of using pytracking.html (example: long emails are often cut off by the email clients and the tracking pixel is thus not loaded).
• Do not replace tracking link with adapt_html