Add remove standup.

Signed-off-by: François de Metz <francois@stormz.me>
Remove args from the standup class.

Signed-off-by: François de Metz <francois@stormz.me>
Rename args property in the hubot script to users.

Signed-off-by: François de Metz <francois@stormz.me>
Add hubot doc about standup remove.

Signed-off-by: François de Metz <francois@stormz.me>