(Basic Completion): Note that read-file-name-completion-ignore-case

(Basic Completion): Note that read-file-name-completion-ignore-case
and read-buffer-completion-ignore-case can override
completion-ignore-case.
(Minibuffer Completion): Document completing-read changes.
(Completion Commands): Avoid mentioning partial completion mode.
Document minibuffer-completion-confirm changes, and
minibuffer-confirm-exit-commands.
(High-Level Completion): Document new require-match behavior for
read-buffer.  Document read-buffer-completion-ignore-case.
(Reading File Names): Document new require-match behavior for
read-file-name.