NEW FEATURES / ENHANCEMENTS:
feat: support new SQL query syntax.
feat: add new meta-database for keeping all the metadata in the cluster.
feat: support event-driving stream computing.
feat: provide a whole new message queue for sub/pub time series data.
Feat: remove the restriction for several query syntax.
enh: provide the cloud-native architecture of TDengine.
enh: employ Raft protocol to ensure the consistency in distributed environment.
enh: utilize the B+tree to keep the meta-data in vnode.
enh: add invert index for the fast search of the tag data.
enh: improve the launch speed significantly.
enh: support keep 1 billion time series data in a cluster.
enh: provide a configurable cache to hold the latest data with various types.
enh: develop a new data transporter to between different nodes in the cluster.
enh: utilize the distributed hash table to locate the table to variable nodes in the cluster.
enh: support roll-up SMA for super table to down-sample the raw time series data.
enh: support time interval SMA to provide the approximate the time window aggregate result.
doc: provide an new user manual, including SQL syntax usage and cluster maintenance.