could not parse '' to 'System.String'

[aspark]

1. fix exception when parse "app -n" via Setup('n',..)
   Exception: could not parse '' to 'System.String'
2. add option execute sequence support. assign the the property ParseSequence when create a parser. the default value is same as the setup register order.

[siywilliams]

I'm manually merging this into the 1.5 branch as the commands functionality has caused some conflicts here.

[siywilliams]

Merged manually into 1.5/develop.

thanks @aspark