Added a command to load reload a bin at least once

This is just a preliminary command to load a bin while using something like malloc://.  Basically, this will free the current bin (r_core_bin_free), create a new bin (r_bin_new), set the current core, and then call bin_load.  I believe this will only work for malloc:// atm.  this does not try to clean up the core at all, there is other stuff that would need to be fixed up, like asm, anal, etc.