Refine QueryExpr and add preliminary support of pipe syntax, only FROM, SELECT, WHERE

[apstndb]

Refine QueryExpr to able to support upcoming pipe syntax.

It requires breaking change of top level query structure.

Breaking changes

• It introduced ast.Query and move WITH, ORDER BY, LIMIT clause into it from ast.QueryStatement and other ast.QueryExprs.
• ~It introduced ast.AllOrDistinct interface, it replaces distinct in ast.Select.~
• It introduced ast.AllOrDistinct typed string. it replaces distinct in ast.Select and ast.CompoundQuery.

Related issues

• close #199
• close #203
• close #204