refs #64: Added memoization around certain expensive operations.
refs #64: Update note
refs #64: Something odd with el_iter in 2.7
refs #64: fixed typos, added memoization, set() are significantly faster than lists (in this case)
refs #64: Update note
refs #64: Simple name change.
Merge pull request #64 from OpenScienceFramework/issue_64

Performance issue on large tables with many table cells