Trying to debug a memory error, also added a set intersection function
for Yale (experimental)
Finally got to the bottom of memory error.
  * Fixed double-free problem (by @cjfuller)

  * Fixed contiguous array marking fencepost error

  * Fixed C/C++ API compatibility problem preventing rb/gsl linking

  * Resolved a number of compiler warnings, including one return-type
    problem that would likely have become a garbage collection error
    (if it wasn't already)

  * Fixed -O3 optimization

  * Added experimental #yale_row_key_intersection function for expert
    recommendation problems