Raise NotImplementedErrors where appropriate
Replace "childs" with "children"

This commit introduces some breaking changes to the DSL and API:
- :childs_update_period => :children_update_period
- StopChilds => StopChildren

The child process polling loops have been tightened up in a few specs to
reduce/eliminate spec failures due to awkward timing.
Clean up language in logger calls

This is an attempt to make the log output a bit more consistent and
readable for native English speakers.

- PIDs are always displayed as "<PID>"
- Tuning/debugging suggestions are made in the second-person
- Actions are reported in present tense
- Results/failures are reported in past tense
Consolidate multiline error messages
add smile not to forgot notify here
fix self pid
fix trigger docs
some messages fixes
Merge branch 'pr/37'