implement NDELAY option

[goatshriek]

Stumpless currently does not support the STUMPLESS_OPTION_NDELAY option despite providing it in its header files. This option is meant to mirror the LOG_NDELAY option in functionality. The meaning may change across target types though - this will need to be thought through, defined, and documented for each of the target types.

Don't forget to document the option after you implement it in include/stumpless/option.h.

Check out the Contributing Guidelines and the development guide for the basics on working with stumpless and submitting changes.