A random assortment of documentation additions.

Visibility housekeeping: reduce to least access level.

Remove synthetic accessor method generation by increasing visibility.

Remove redundant double-cause initialization.

Remove needless unchecked suppression.

Add Call.Factory for alternate HTTP client implementations.

Switch to a proper builder for MockRetrofit.

This allows passing an explicit executor for test cases.

Throw normal IOException when canceled to match OkHttp.

Remove incorrect generic parameter.

Correct `@Path` documentation.

* Clarify that replacement happens in a single segment.
* Reference the `encoded` property correctly.

Add missing Call wrappers as return type

Correct some Javadoc examples, always run Javadoc plugin.

Add test for executing Calls at most once

Introduce new mock pattern with a behavior delegate.

This allows the mock implementation to only concern itself with the response type and the BehaviorDelegate will apply any delays from NetworkBehavior and also run through the Retrofit's CallAdapter.Factory list to turn the delayed Call into the appropriate type that matches the return type of the method.

New package name for version 2.

Support iterable and array types for `@Part`.

Move tests to same package as tested classes.

Allow converters to delegate to others.

Add a sample for this in the form of one that forces chunked uploads when `@Chunked` is added to `@Body`.

Add converter for scalars to request body.

Add isExecuted method to Call.