shelve: add minimal documentation to all functions There is a lot of functions in this extension. We had a small documentation help people getting started.

shelve: use the class constant in the clear method This class attribut is used everywhere else. Not using it in clear will get us in trouble sooner or later.

hgweb: fix unstoppable loading of graph when no more results When a user reaches the end of repo history with graph view, it (unsuccessfully) tried to load more entries. This patch disables further loading attempts.

hgweb: remove now unnecessary explicit header() and footer() They became unnecessary after allowing custom-named entries in templates.

hgweb: replace 'shortlog' with 'changelog' in raw changelog template

shelve: drop pickle usage Pickle was used to the `shelvedstate` file. However the content of the file is very simple and we can handle serialisation ourself. Not using pickle is a net win. Note incrementing the format version as no releases have been done so far.