Updating docs for range operators

[austindrenski]

This updates mapping-and-translation.md to reflect #323.

• Changes "datatype" to "data type" per the PostgreSQL docs
• Changes [Column] to ColumnAttribute (the bracket form is already in the example)
• Adds some inline code formatting (e.g. "string" to string)
• Adds inline code formatting to the table entries

[roji]

Thanks @austindrenski, it's great to get some docs contributions as well.

I'm merging your PR, but in fact I was planning on creating a separate page for ranges only. I'm pretty sure most users coming to Npgsql EF Core simply aren't aware of PostgreSQL ranges, and would benefit from a page concentrating information on them.

[roji]

See https://github.com/npgsql/Npgsql.EntityFrameworkCore.PostgreSQL/blob/dev/doc/mapping/range.md for a separate page I wrote for ranges.

(I plan to clean up the entire documentation a bit for the RTM...)