Enhanced option parsing

[seeruk]

It'd be great to have better short option parsing, so that they could be grouped up -abc (is this option folding?)

It'd also be great to not have to put an = in after an option for ones that could/should have values (i.e. look ahead in the argument list, and consume arguments as option values).

To accomplish this, it might mean that input parsing and mapping have to be done in the same place. The context that is in mapping would be useful for parsing. Alternatively, if there's a way of doing some quick checks to help parsing make better decisions before mapping that might work too.

[seeruk]

Needs tidying up, but both option folding and specifying option values without = work in branch feature/opts-without-equals.