Removed C-v bindings; they were inconsistent.

Removed C-v bindings; they were inconsistent.
Defvarred some variables to nil, solely to avoid compilation warnings.
Use "Author's Update Number:" instead of "Version:".
(bookmark-history): new var.
(bookmark-completing-read): use `bookmark-history'.
(bookmark-historicize-string): new macro.
Use this everywhere `bookmark-completing-read' is used, because
`completing-read' won't get a chance to add to `bookmark-history' if
we were invoked via a menu.
(bookmark-rename): use `bookmark-history' when reading the new name.
No need for the strange C-o binding anymore.