don't load test dependencies in Python 3.3 that don't work in Python 3.3

… without valid users

coerce user attributes into strings when necessary, don't send events without valid users

…ration

ensure that client components are cleaned up correctly in every configuration

miscellaneous test fixes

# Conflicts:
#	ldclient/client.py
#	ldclient/flag.py
#	testing/test_ldclient.py

support metric value with track()

allow unit tests to be run without databases

update readme format and repo links

(big segments 3) implement big segment status tracking, wire up components

…er-sse

better SSE implementation that fixes linefeed and multi-byte char issues

…ests

implement SSE contract tests for Python

…ctor db tests (#158)

update mypy version

fix big segments user hash algorithm to use SHA256

…empty

more Big Segments fixes