refactor: extract concurrent query count function from FilterChainProxy
into a filter.
Merge pull request #31 from cnnic/dev

merge from cnnic
refactor: add QueryFilter - pre/post param validate, and post query
filter; move original filters to 'http filter'; move
acl/policy/ResponseDecorate to query filters, and this filter can
support service such as 'limit/forbidden domain' policy.
move policy to query filter package.
Merge pull request #523 from forumbyr/master

refactor, see commit details .