Fixing SP500 size and correctness issues
 * Removing cached SP500.html file. This was causing the SP500 to be old
 * Setting the current number of symbols to 502 because of the addition of class C shares
 * Fixing a bug where we could not download the sp500 correctly in python2
Cleanup code for finsymbols.
 * Remove is_connected method. It wasn't really doing anything and was
   just slowing our retrieval down
 * Remove csv files and csv fetching methods. They were unnecessary
 * Remove additional README.md. It was outdated and we don't need two.
 * Add .gitignore to exchanges dir so that the dir will be created when
   we clone the repo
Removing exchanges dir. It would've just gotten in the way in the case
of a virtualenv installation