* ampc.el: Take window width into account when computing tabular cell widths.
(ampc-views): Replace :offset by :min, :max and :width properties.
(ampc-tab-offsets): New variable.
(ampc-pad): Use ampc-tab-offsets to pad input. Do not accept an alist any
more. All users of ampc-pad changed to reflect the new format.
(ampc-update-header): Move "[ Updating... ]" label to the front of the header.
(ampc-set-tab-offsets): New function.
(ampc-configure-frame-1): Call ampc-tab-offsets to compute the tabular cell
widths.