Use stderr and return codes >0 when it makes sense.
Loose return code conventions:
* 1 for generic errors
* 2 for user input errors
* 3 for remote errors (not found, etc.)
* 4 for not implemented

Maximum number of revisions in iter_revisions is now 500, the API's limit
for normal users.

webcontentedit has been updated to use the 'count' option for do_log().

This new command displays the last revisions of the page.

TODO: specific formatter (it should display the history like git log).