CREATE STREAM should support column names starting with @ when reading from JSON

[my2ndhead]

Some json documents may contain elements starting with a @-character.

Example query:

CREATE STREAM filebeat_original (@timestamp VARCHAR, message VARCHAR) with (kafka_topic='filebeat', value_format='JSON');

Example json:

{ "@timestamp": "2017-12-19T15:37:55.184Z", "@metadata": { "beat": "filebeat", "type": "doc", "version": "6.1.0", "topic": "filebeat" }, "offset": 14619691, "message": "Dec 19 16:37:54 www kernel: ...snip...", "source": "/var/log/messages", "prospector": { "type": "log" }, "beat": { "name": "www", "hostname": "www", "version": "6.1.0" } }

ksql should support the @ character in column names, allow substitution characters or renaming columns on-the-fly.

[hjafarpour]

@my2ndhead I pushed a fix for handling fields with @ prefix. Please try the latest version from master branch and let us know if you find any issues.