and writes. This was previously unsafe because we almost always passed read/write
buffers to boost that were on the stack. Canceling the task deleted the stack and
therefore the buffer, but couldn't reliably prevent boost from writing to the buffer
if data came in after the cancel. This commit adds variants of the read and write
functions that take a shared_ptr<char> instead of a raw char* as the buffer, and
these variants will ensure the shared_ptr will outlive the boost::asio read/write.
