Add class-based-testing fixtures and decorators

This should ease testing on legacy class-based test suites that
don't want to switch to function-style test
bump version
DESCRIPTION.rst: code blocks + wrap text
Add test_httpbin_accepts_lots_of_get_requests_in_single_session

This test is actually failing for me at least part of the time on py34.

This was inspired by a bug in httpie:
https://github.com/jakubroztocil/httpie/issues/278#issuecomment-65005675
setup.py: Get version from version.py

This creates a new file, pytest_httpbin/version.py and makes setup.py
execute that file rather than doing an `import pytest_httpbin` which
causes the setup.py to depend on pytest being installed.

Fixes: #9
tox.ini: Add py33 + format tweaks

Support py33, because the tests pass, so why not? :)
Add cleanup_headers to ServerHandler

that adds `Connection: Close` response header so that clients don't
expect keep alives.

Fixes: #13
Support providing arguments to tox posargs

E.g.:

    tox -e py34 -- --tb=short -k test_httpbin_accepts
Merge pull request #16 from msabramo/fix_lots_of_requests_in_single_session

Fix lots of requests in single session
Merge pull request #15 from msabramo/tox_py33

tox.ini: Add py33 + format tweaks
Merge pull request #14 from msabramo/versionpy

setup.py: Get version from version.py
Merge pull request #12 from msabramo/update_DESCRIPTION.rst

DESCRIPTION.rst: code blocks + wrap text
add fixture httpbin_ca_bundle

Configures the pytest_httpbin ca bundle
use httpbin_ca_bundle in our testsuite