add star schema benchmark

[zz-jason]

1. There are 5 tables in the Star Schema Benchmark, table schemas are defined in create_table.sql, I wrote them one by one according to the paper, please check them carefully.
2. There are 13 queries in the Star Schema Benchmark, listed in directory queries, I pasted them from the same paper
3. dbgen is taken from electrum/ssb-dbgen, with the following modifications:
   • fix build on linux, see Linux compile problem electrum/ssb-dbgen#1
   • fix some typo, see Fix typos electrum/ssb-dbgen#7
   • fix some compile warnings

@zimulala @shenli PTAL

[ngaut]

LGTM

[winoros]

Any current result of this benchmark?

[zz-jason]

@winoros No, you can have a try.

[shenli]

LGTM
We could add this to the bench_bot.

[zz-jason]

I have made a simply test on these 13 queries with scale factor 1, all of them are executed within 3s. Their test scenario seems simpler than TPC-H