sleeper 0.4.0

• Added sl_example_model() to bundle compact fold-2 example in package.
• Updated the runnable sleep-estimation example and tests to use a short data segment and compact models.
• Reduced the example-only forests to one tree each to keep CRAN example CPU time below the checking threshold.

sleeper 0.3.0

• Initial CRAN submission.
• Added in ability to download individual models