Added a "format_extract" UDF.
Added a "format_extract" UDF.

The format_extract function takes three arguments:
 1. the FORMAT field from a VCF
 2. the sample field from a VCF
 3. the name of an attribute listed in the FORMAT field

All three are strings.

It returns a string which is the value of the attribute, from the sample field, whose name matches the third argument.

Paradigm4/load_tools,Paradigm4/load_tools