Remove exception_log from MetaInspector::Document#defaults

This was causing a bug where :warn_level options was not being properly
honored. Given that we already instantiate an ExceptionLog, just do so
as the default.
Test Document#(<url>, warn_level: <warn_level>) behavior

Update specs to test only behavior of public methods
Merge pull request #95 from jgandt/fix_document_warn_level_default

Remove exception_log from MetaInspector::Document#defaults
cleans up specs. Improves #95
removes defaults from all classes except Document. Improves #95 and #92
improves specs for exception handling in Document.

We better avoid memoized helper methods in these examples, and also test that
warnings really appear on STDERR (while avoiding cluttering rspec output).

Improves #95
release 3.2.0
Add link to Gitter room in README
Include link to Google group
reviews example scripts