create set of fixed slots based off of numprocesses

allow reuse of slots as Process objects are reaped
modified the sigterm/sigkill dance - refs #515
added an async flag
more async fixes
forgot to pass some options
give the CPU a break
fixed flags
quit has to be synced
SIGHUP can be asynced
Revert "create set of fixed slots based off of numprocesses"

This reverts commit aea929e7e6ca679b09d8fe4e0e2af08a747bc6d5.
supply a worker id that tracks w/ numprocesses

worker id's are reused as their corresponding process is reaped
a new property is added: "Watcher.nextwid" which returns the lowest unused worker id number
name change for nextwid

implied private property
removed unused var
added the async option to quit
missing opts parsing - +need test
added --async support to quit
more hints on timeouts
make --async a generic command pattern
more async fixes
simplified implementation