Rscript parses the whole file before executing in order to be able to respond to `materializeInstrumentableNodes`

* New interface RootBodyNode implemented by FunctionBodyNode
* FunctionBodyNode saves args and then executes the actual body node
* New tag FunctionBodyBlockTag that tags BlockStatements that are function bodies
* FastR debugger that used to listen to RootTags (originally BlockNodes that had FunctionDefinitionNode as parent) is now listening to FunctionBodyBlockTags

- fixes

Additionally restructured the Rembedded.c file to logical blocks, add visual dividers, clean-up the code.