The goal of breaking apart the base_parser() function is to get rid of
a bunch of conditionals and parameters in the code and, instead, make
code look like simple composition.
When splitting, a choice had to be made as to whether this would operate
by side effect (modifying a passed in parser) or side effect-free
(returning a new parser everytime).
Making a version that's side-effect-free appears to be fighting with the
optparse API (it wants to work by creating a parser object, configuring
the object, and then parsing the arguments with it) so instead, make it
clear that our helper functions are modifying the passed in parser by
(1) not returning the parser and (2) changing the function names to be
more clear that it is operating by side-effect.
Also move all of the generic optparse code, along with the argument
context classes, into a new subdirectory.
* Once cli args are parsed, they're constant. So, save the parsed args
into the global context for everyone else to use them from now on.
* Port cli scripts to use the CLIARGS in the context
* Refactor call to parse cli args into the run() method
* Fix unittests for changes to the internals of CLI arg parsing
* Port callback plugins to use context.CLIARGS
* Got rid of the private self._options attribute
* Use context.CLIARGS in the individual callback plugins instead.
* Also output positional arguments in default and unixy plugins
* Code has been simplified since we're now dealing with a dict rather
than Optparse.Value
