Add Makefile

Instead of using autotools, a Makefile was added.

v0.11: del warn(NULL)

The message displayed by `warn(NULL)` makes no one happy.

v0.10: add option -f

Specifying the target MAC addresses each time is tedious and prone to
mistakes.  The method of using database files to look up MAC addresses
solves this problem.

v0.02: fix SO_BROADCAST

Because the valiable `yes` was not initialised to non-zero,
the option `SO_BROADCAST` was not set correctly.

v0.01: Renew All

The first version of sendwol.