sets a per_page default to 100 if None is specified, addresses #128
Improve fix for #128
Improve UnitHelper

- Delegate creation of instance to an overridable method
Add doc-string to TestRepository#test_asset unit test
Last iteration for #128 and unit test for it
Smarter per_page modification

- Re-record cassette for iter_languages
Fix tess/test_gists.py
Fix tests/test_github.py
Fix tests/test_structs.py
Fix tests/test_orgs.py
Fix tests/test_repos.py
Re-record cassettes that were failing
Ensure that per_page is never -1
Failing test around PR #176
Return the empty string for empty gitignore templates

Let's not crash trying to interpret None as json, but return an empty
string instead.
Merge pull request #168 from sigmavirus24/feature-fix-126

Feature fix #126
Document how to run the tests with credentials
Remove legacy search API
Remove legacy search classes
Remove legacy search API from github3 namespace