Consider adding support to define remaining data size

[joachimmetz]

Consider adding support to define remaining data size

name: mru_value_string_and_shell_item
type: structure
attributes:
  byte_order: little-endian
members:
- name: string
  type: string
  encoding: utf-16-le
  element_data_type: wchar16
  elements_terminator: "\x00\x00"
- name: shell_item
  type: stream
  element_data_type: byte
  elements_data_size: <<remaining data size>>

Maybe instead of a structure use a format data type?

Do this via context() instead?

Current method of doing it would be to read string, determine the byte size using the context and use that as the byte offset.