winhelp: Fix the loading of a row in a table (especially, for multiple paragraphs in a single cell).

winhelp: Added the notion of WINHELP_WNDPAGE and use it to move the history to the global variables.

winhelp: Get rid of the reuse concept for Windows and refactor the code a bit for window creation / deletion.

widl: Remove duplicated code in the form of the write_struct_expr function by enhancing write_expr to allow toplevel identifiers to be prefixed by a string, if specified.

Remove the conversion of pointer types into base types as this was only 
needed due to lack of proper type resolving.