tidb-server v1.0.6

• Support the Alter Table Auto_Increment syntax
• Fix the bug in Cost Based computation and the Null Json issue in statistics
• Support the extension syntax to shard the implicit row ID to avoid write hot spot for a single table
• Fix a potential DDL issue
• Consider the timezone setting in the curtime, sysdate and curdate functions
• Support the SEPARATOR syntax in the GROUP_CONCAT function
• Fix the wrong return type issue of the GROUP_CONCAT function