new maintainer for Shelve extensions

[TK Soh]

Greeting. Just to share that, due to my other commitment, I'm becoming
a burden to the development of the Shelve extension. And thanks for
Oleg Oshmyan (chortos at inbox.lv), who has been kind to take over as new
maintainer of the extension, effective immediately.

The repository has been transferred to Oleg:

    https://bitbucket.org/astiob/hgshelve

The wiki page has also been updated to reflect the changes.