Changed a few 'describe's in specs to 'context's

Two are equivalient in rspec, just for semanitics / consistency
Cleanup node class / extract node_callback into seperate module

No functional changes. Adds complete spec suite testing all
node and node_callback edge cases
Split logger & core_ext modules out of lib/rjr/common

No functional changes
Remove unused semaphore class
Add new Argument object to encapsulate specified json-rpc args

Also defines various helper methods to query / extract data
from argument set
Make Arguments instance available in request context
Small JS Fix: ensure socket created before attempting to close
Remove unused errors module
Add HandlesMethods mixin to define structured handler classes

Now in addition to registering free floating procs w/ dispatcher,
dev can register handler classes containing encapsulated dispatching
logic for one or more json-rpc method signatures