For nearly all commands in U-Boot the '?' variable is handled the same
way with 0 meaning success, 1 meaning any failure.  Explain this in the
general rules section of the cmdline documentation (with a link to a
counter example) and then remove the redundant wording from most
commands. We retain a section about the return value in a number of
places where we are doing something such as always returning a specific
value or we have useful additional information to go along with the
normal return codes.

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>

Describe the env command.

Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>

U-Boot mostly uses hex for value input, largely because addresses are much
easier to understand in hex.

But in some cases a decimal value is requested, such as where the value is
small or hex does not make sense in the context. In these cases it is
sometimes useful to be able to provide a hex value in any case, if only to
resolve any ambiguity.

Add this functionality, for increased flexibility.

Signed-off-by: Simon Glass <sjg@chromium.org>

Mention the default base of U-Boot in the command-line section. Add
examples for decimal and octal.

Signed-off-by: Simon Glass <sjg@chromium.org>

Take this part of the README and put it into rST format.

Signed-off-by: Simon Glass <sjg@chromium.org>