Implemented new signal name/num lookup functions

Wrote a perl script that generates the table from sig_list.txt.
The new signame function does not return a full signal name,
and requires more code to use it (check for null, apply prefix)
but it kept the signal names smaller than 8 chars, so I can use
int64_t to compare them.

fixes #17  refs #16
Refactored previous patch

The lookup routines are now in signal.c, and only the lookup
table is generated by the perl script.

Also fixed references in controller.c that use these methods.
Testcase for service.start, and fix signal mask before exec

The child processes were inheriting their parent process mask,
making them ignore most usual signals.

Fixed that, and also made the default filedescriptors /dev/null
instead of closed, when no service.fds was set.

refs #4
Added service.signal command

One testcase still failing is sending the signal to process
group.  Need to investigate that one.  The process exits,
but kill() returns an error.

fixes #16