Updates documentation for configuration

This updates the documentation to contain explanations of most configuration
options that can be specified in client.cfg. I tried to include as many as
possible, but I've probably missed some. I grepped the code to try to find all
of them. For completeness, these include my best understanding of how each
parameter works. Many descriptions are therefore incomplete and need to be
filled out better by people who understand them.

Some descriptions may be wrong, but only in ways that reflect the understanding
an average user would have after reading the code to figure out how to properly
configure luigi. So this shouldn't be any worse than what we already have even
where it's inaccurate.
Merge pull request #509 from Houzz/config_param_docs

Updates documentation for configuration
initial RangeHourly implementation

Efficiently produces contiguous completed ranges of recurring tasks.

Already in:
* RangeHourlyBase general API
* RangeHourly subclass which automagically facilitates filesystem listing
  as the most common case. Supports tasks with multiple outputs and, as a
  convenience, WrapperTask hierarchies as well
* Convenient CLI usage

Coming soon:
* Events emitted with relevant metrics
* RangeDaily/Weekly/X-ly generalization
* More sanity checks to behave gracefully when preconditions aren't
  satisfied

Wishlist:
* More common cases facilitated, that are not like filesystem listing