Add movement to starting position in `seq.scan()`

[BrianJKoopman]

Sometimes scans have accidentally been started in an incorrect location. Adding a starting position argument to seq.scan() and calling acu.move_to() within seq.scan() might mitigate the issue.

[newburgh]

I like this option; I definitely prefer to know the az/el the telescope is going to, which is solved if its an argument in the scan command. This requires a small modification to runlib and the scheduler?

[BrianJKoopman]

I like this option; I definitely prefer to know the az/el the telescope is going to, which is solved if its an argument in the scan command. This requires a small modification to runlib and the scheduler?

Yup, implemented in #191 as an optional argument to seq.scan(). The scheduler can then start to use this whenever convenient.