adding load_path to include active_model in the load path of example

No reason to decompose the join objects on every iteration

the @reflections ivar.

We should consider moving the input munging outside the class
instantiation

Stop typechecking the parameter.  We know the type.

The reflections hash is supposed to be private, so let's use the API.

`instantiate` is only called once, so there is no reason to cache the
data structure on the instance and mutate itself.

similar to activerecord/examples/simple.rb

Call `rails plugin new yaffle` in the plugins guide. [ci skip]

It's confusing to not explicitly do this step.

We know the structure passed in to the `construct` method will be a
hash, so we don't need to test it all the time.  The key value will be a
symbol or string, so handle it with the special method

We control the inputs to `construct`, so the wrong type shouldn't be
passed in ever.

different threads.

This is to be consistent with the way the mysql2 adapter times queries

Fixed typo in documentation

Directory name in RUNNING_UNIT_TESTS.rdoc [ci skip]

We always know the parameters in advance, so we don't need to build it
in to the method signature

We always set the join type immediately after construction, just make it
part of the constructor and we can skip that step