fix length calculation
more thorough tests for composite fields
allow subfiels for #17
refactor common FieldParseInfo creation code
work on #20 optional CustomField in FieldParseInfo
improvements to CompositeField
Parse fields with subfields in parse guides for #17
Fix #20 use FieldParseInfo's own CustomField if available
binary property is gone
tests for #17 from xml config
test for #17 from xml config