Unfortunately, copyright and legal issues with publishers and copyright holders restrict us from including melody and lyrics. 
iReal Pro supports transposable chord charts with play along function.
There is a possible solution on certain iOS and Android devices.
iReal Pro 7 and higher supports multitasking (split view) on newer iPad models. 
You can read PDF music charts while using iReal Pro.
More info about multitasking:
Some users are using a PDF viewer app with either the chart from iReal Pro as PDF (you add text, lyrics etc. to the PDF) or PDFs of your existing charts (from Real books etc.) and if you need iReal Pro backing, this can be run in the background.
This method is discussed in the iReal Pro Forums here.
You can export any song in music XML format, open it in a music notation software (e.g. Sibelius, Finale, MuseScore) and then add melody/lyrics.

Some users have found ways to add lyrics using the staff text in the editor.
See their solution here.