bump ichannel dependency to ~> 5.2.0
documentation improvements.
update gemspec
update ChangeLog.txt
bump ichannel dep. to v6.1.1
retain Process#frequency between restarts.

Closes #33.
add XPool#restart
README - todo: redis.
readme update
add XPool::ProcessStatus.
delegate to XPool::ProcessStatus
handle nil values
add first_run?
process goes available right after fork.
docs
cleanup test condition logic.
simplify. revisit implementation of lost features later
todo
invoke Unit#recover() on exception.
docs