use Test::Nginx::Socket::Lua instead of Test::Nginx::Socket in our test suite so that we can run existing tests with lua-resty-core.
added more (passing) tests.
bugfix: the memcached connection might enter a bad state when read timeout happens because ngx_lua's cosocket reading calls no longer automatically close the connection in this case.
fixed the test plan in mock.t.
optimize: eliminate one (expensive) string.sub() call in the redis reply parser.
fixed a test case that could fail in slow testing mode.
doc: updated the copyright year.
bumped version to 0.18.
merging with master