fixing bugs in WinApi plus some extensions. Refs: #23.

Changes as proposed by Koen Desaeger and Helmut Zinn in CPC_1.7 rc4.
Change all occurrences of WINSPOOL.dll to WINSPOOL.drv (Helmut Zinn)
Change all occurrences of VAR [nil] lpData: SHORTCHAR => lpData: PtrVoid (Koen Desaeger)
Change WM_KEYLAST* = 265; to WM_KEYLAST* = 264 (* {3, 8} *);
Some constants and procedures have been added.
Some comments are added in order to describe the intended data type.
The default variant of a procedure which exists in two forms, one for ASCII and one for Unicode,
has been enclosed in fold elems.

Signed-off-by: Josef Templ <josef.templ@gmail.com>