Improve SELECT/PERFORM/RETURN formatting

[joelmukuthu]

Closes:

• Discussion [postgres]: ideal way to format SELECT/PERFORM statements with a single column? #75 -- SELECTs and PERFORMs with a single column have the column printed on the same line. Most of the changes relate to updating existing tests to match the new formatting
• Improve RETURN statement formatting #79 -- hanging indentation for long RETURN statements. I didn't touch RETURN NEXT though as it wasn't in the issue and I imagine this fix is not necessary for it as it doesn't usually return boolean expressions.