Compare 2 tables

Create module compare.py which compares tables.

Sample usage would be like below

```
c = rawdata.compare.Table(tbl1, tbl2)
> c.cols
> [all columns the same]
> c.rows
> tbl1=6050, tbl2=6201, result=98%, outcome=OK
> c.values('year')
> tbl1.yr=[2014,2015], tbl2.yr = [2014,2015,2016], result = 66%, 1 extra val, == OK
```
