conferences: Rename Boston file to match others

The link was broken in the README, this will fix it (by following the 
same naming convention as the other files.
bos2013: Fix pydata.org URLs, add video links

This removes the extra ‘/‘ in the pydata.org urls and adds links to my
videos and slides.
Merge pull request #4 from mdbecker/master

conferences: Rename Boston file to match others