Additions and changes to field modifying functions.

• record_delete_subfield_from(), record_add_subfield_into(), record_modify_subfield(), record_move_subfield() : new functions which performs operations on subfield specified by field number and subfield index.

• Unit tests added for new functions.

• record_delete_field(): field number is now checked correctly, tag is deleted if last field in tag is deleted.

• Added calls to wash_indicators() and updated indicator default values.