Add support for FB record format #420
Description
Background
Currently, Cobrix supports: F, V, VB and D formats. The only record format missing is FB
Feature
Add support for FB record format
More on record formats: https://www.ibm.com/docs/en/zos/2.3.0?topic=files-selecting-record-formats-non-vsam-data-sets
More on FB format: https://www.ibm.com/docs/en/zos/2.3.0?topic=sets-fixed-length-record-formats
More on BDW: https://www.ibm.com/docs/en/zos/2.3.0?topic=records-block-descriptor-word-bdw