Cutover to using 'pos' from the FSharp Compiler Service library - thereby avoiding conversions / duplicated position representations.
As I'm using the sentinel footer for the overall structure YAML, may as well remove it from the 'OverallStructure' type, thereby avoiding potential bugs.
WIP: now generating synthetic child terminals for the overall structure to include extraneous file contents not covered by the complete abstract syntax tree. Also laid some ground for fusing adjacent children to cover the span of the enclosing parent container, this part is not yet finished.