Error on invalid option, add support for -- to ignore further options
Add new 'state' command, bump version to 2.8

'state' outputs a list of times relative to time-start that define how long
the system has been in each state. It supports both percentage output and raw
seconds output. Its output format is:

  <beginning state>
  <length of state 1>
  <length of state 2>
  ...
  <length of state n>

* Each state alternates from the one before it, so if the beginning state is
  'up' then the first state length is the length of time the system was up,
  followed by how long the system was down, then up etc.
* <beginning state> is a simple string defining the state at the beginning.
  Possible options are 'up' and 'down'.
* In percentage mode, the 'length' of each state is a percentage of the total
  time specified by time-start and time-end.