Supporting general group by

[Mestway]

We want to enable Cosette to handle the following new forms of aggregation query forms:

• Allowing select fields to have different orders (now we only support aggregation functions in the last)
• Supporting operations over aggregation columns.
• Support having functions.

An demonic example is shown below.

Select a, max(c), b + 1, count(*) + 2, min(a + b)
From  t
Group by a, b 
Having min(d - a) > 2

[Mestway]

Rosette side support done, the rest is to add parser support. Interface use example can be find at rosette/tests/denotation-test.rkt.