I'm submitting some additional -dwim functions to that change the
capitalization of text the way the user probably wants.

These work similarly to comment-dwim, or count-words: they act on the
region if and only if it's active (more specifically, if (use-region-p) is
true), and otherwise act on the word starting at point. Either way, they
use existing functions in Emacs: e.g. #'upcase-dwim delegates either to
#'upcase-region or #'upcase-word.

There are three functions: one for each of capitalizing text, upcasing
text, and lowercasing text. The docstrings are based on the docstring for
comment-dwim.

In my init file, I've changed the default mappings of M-u, M-l, and M-c to
these new functions, and would support changing Emacs's defaults to them.
However, I am led to believe that changing defaults isn't preferred, so
this patch doesn't contain any of that. Even without changing defaults, I
believe these functions are worth adding to Emacs.

The capitalization-related functions I'm using are all defined in C, so I
can't put these new functions alongside them. I put the changes in
simple.el, as that file's described as "A grab-bag of basic Emacs commands
not specifically related to some major mode or to file-handling.". I'm
happy to move the functions and create a new diff if there's a more
appropriate file for them to live in.

Changelog entry:

* simple.el: Add functions for capitalizing text intelligently.
(capitalize-dwim): New function.
(upcase-dwim): New function.
(downcase-dwim): New function.

The diff is attached.

-Zachary Kanfer