[REVIEW] Initial fixed_point Column Support

[codereport]

This is part 1 of adding support for fixed_point columns. The follow up PR will:

• Add scale_type into data_type
• Hook up the thrust::transform_input_output_iterator
• Customize allocation factory functions (to only allocate for underlying value)

Still to do for this PR:

• Disable support for certain algorithms
• Add numeric::decimal64 and corresponding code
• Make unit tests general to include decimal64
• Get binaryop working for decimal64

[harrism]

Great work @codereport ! Just add that one comment about why simt::std in fixed_point.hpp, otherwise good to go.