cleaned up the code from 2012, fixed the attachments in some of the 2013 events.

content/events/2012/nebraska_supercomputing_symposium_12.md

content/events/2012/supercomputing_mini_workshop_2012.md

content/events/2013/hcc_matlab_workshop_2013.md

content/events/2013/hcc_mpi_workshop_2013.md

content/events/2013/june_2013_osg_workshop.md

...nts/2013/supercomputing_mini_workshop_february_27_2013.md