Special case RealMath in expressions
Add tests for user defined functions and math functions
Test more math functions
sql: map fixlen strings to sqlalchemy.String
sql: properly translate string encoding and length

between datashape and sqlalchemy
expr: Summary
expr: summary hashable and eval(str(.)) able
python: Summary compute
scalar: name, dtype properties
expr: Reductions support Number interface
compute: python arithmetic
python: summary by
pandas: summary by tests
pandas: summary by
pandas: summary
sql: summary and by summary
expr: name attribute for TableExpr

in case a TableExpr is a column
spark: summary
don't test base spark

Sadly we can have only one SparkContext
python: refactor out split-apply-combine reduceby funcs

These will be used in spark