Clarify "estimate" paramter in docstring

I found the description currently in there rather confusing until I went and looked up the documentation on the SDSS site. This just clairfies what `estimate` is for (I'm also using it to try out the "edit" button on github, which I've never used for real before.)
if->of
Make timeout option of `monitor` work

I think this is the intended behavior of the `timeout` option.
added system option to quick
added list_tables method
Merge pull request #1 from eteq/patch-1

Clarify "estimate" parameter in docstring
Merge pull request #2 from eteq/patch-2

Make timeout option of `monitor` work
Merge pull request #3 from eteq/list-tables

Add list_tables function