extend create_desc function to hole of description file

[aspina7]

Could try to make the create_desc function pull together all the necessary bits from tableoftables.xlsx so users dont need to create a description file for datasets by hand at all.
Only problem is that requires step of making a dictionary and/or linking to that (necessary for the variable descriptions part - but maybe we just dont list variables in the help file?)
Might be useful?

[aspina7]

after discussion with @PBBlomquist - we wont be adding each of the variable descriptions to the *_doc.R files (not very useful overview-wise and we should be encourging good use of data dictionaries instead).
So instead I will update this function to read necessary parts from tableoftables and this way create a template roxygen file that users just need to edit.