WIP documentation

- The documentation is cluttered enough as it is with the large number
  of procedures supporting vCard 3 and 4. Split common out into the
  publicly exposed bits and the private internals. This makes it obvious
  which common functionality a client can expect to have exposed on the
  main vcard module.

- Add documentation (WIP) on the vcard3 module.

src/vcard/vcard4.nim

@@ -4,7 +4,8 @@ import zero_functional
 
 #from std/sequtils import toSeq
 
-import ./private/[common, lexer]
+import ./common
+import ./private/[internals, lexer]
 
 type
   VC4_ValueType* = enum