Clarify ambiguous min/max stats for FLOAT/DOUBLE

[asfimport]

Describe the handling of the ambigous min/max statistics for FLOAT/DOUBLE types in case of TypeDefinedOrder. (See PARQUET-1222 for details.)

• When looking for NaN values, min and max should be ignored.
• If the min is a NaN, it should be ignored.
• If the max is a NaN, it should be ignored.
• If the min is +0, the row group may contain -0 values as well.
• If the max is -0, the row group may contain +0 values as well.

Reporter: Gabor Szadovszky / @gszadovszky
Assignee: Gabor Szadovszky / @gszadovszky

Related issues:

• Release Parquet format 2.5.0 (blocks)
• Specify a well-defined sorting order for float and double types (relates to)

PRs and other links:

• GitHub Pull Request #88

_{Note: This issue was originally created as PARQUET-1251. Please see the migration documentation for further details.}