This mod for MCPE was coded during the Pi day (3/14/15).
It uses the Bailey–Borwein–Plouffe formula to calculate the Pi (Wikipedia: Bailey–Borwein–Plouffe formula), and to have a better decimal precision it also uses the decimal.js libary for Javascript made by MikeMcl.
For more information, screenshoots, instructions and download links go to this page: http://desno365.github.io/blog/the-pi-mod/