Implement first version of definitions and runtime

[joachimmetz]

Complete first version of definitions and runtime

• Add support for sequences with a runtime number of elements
• Move data type maps to data_maps.py
• Add byte stream support
• Add character array and string support
• Add elements terminator support
• read definitions in multiple phases
  • parse syntax
  • check if all definitions resolve
• Add metadata support
  • author, year, etc.
• move generator and runtime into separate submodules
• Add constant support
• Add enumeration support
  • define how map to a storage data type?
• Improve elements sequence type
  • validate elements terminator type
• add layout type for base record type such as WMF records, WSI extension blocks, etc.
  • base structure / base record / union / group with base
• Add union support
  • support nameless union - only inside structures
• Allow for custom maps e.g. dfdatetime
• Allow for custom defs
• Add read hints for file IO
• Add write support
• Add format support
  • namespace
  • include / import other dtfabric definition files
• Add support for bitstream formats, such as MPEG, bzip2
• Add support for text based formats, such as PDF, cpio variants
  • Text, octal, hexadecimal integer values