Without using `kbd', each key in the string "<escape>" is interpreted as a
prefix key.

fix #492

`magit-show-refs-popup` and `magit-dispatch-popup`
have been renamed without "-popup".

Define magit-show-refs as a transient command
https://github.com/magit/magit/commit/c3135cdb23e223ebf8f3c802616ebb81103fdbe9

Define magit-dispatch as a transient command
https://github.com/magit/magit/commit/dde9a5b77a483fa35d932aecd22c1a4c954ce77e

And make the docstring more readable,
with the related key and command on the same line.

This change adjusts the formatting of the instructions in the `git-rebase`
buffer to allow them to be properly formatted when git's `core.commentChar` is
set to `%`.  In particular, lines will look something like this:

```
%-8s p
```

The root cause seems to be the how the lines are constructed: comment characters
are directly added to the format string.  When it is `%`, `format` appears to
proceed until it finds the next `%` character, (corresponding to the `%` in
`%-8s`) above and prints it directly to the string rather than interpreting it
something to format.

This is fixed by constructing the format string with the comment character as an
argument to `format` rather than being added directly to the format string.

Fixes #468.

"O" is used to launch `magit-reset`, not `magit-revert`. "_" and "-"
should be used for the suffix commands to be consistent with the
prefix key "_".