Add recurly.SOCKET_TIMEOUT_SECONDS attribute

This provides a mechanism of setting a socket timeout specific to
the Recurly module. Without this, it is only possible to set
timeouts using socket.setdefaulttimeout, which affects all calls
to socket in the current Python process.
Drop getattr form since default is specified
Timeout on requests as well as socket open
Merge pull request #68 from thieman/tnt-socket-timeout

Add recurly.SOCKET_TIMEOUT_SECONDS attribute