Provide output information to hint and how to resolve

[hamishwillee]

It would be useful to provide information about how to resolve errors in the output log:

Proposal is to add two (optional) new fields:

<hint>Brief hint about how to resolve, where to go for more information</hint>
<resolution-url>url</resolution-url>

The resolution-url should be configurable in a config file.

The "hint" would be used for cases where a basic string may be enough to resolve the issue. For example, there is nothing a user can do if they see "Any Parameters Seen" - its a problem with the log itself. In this case a hint of "There is no action a user can take to debug this error" might be useful. Similarly if you get the Vehicle Definition error a hint to specify the -m and -f in logs would be useful.

The resolution-url is intended to provide an URL to a page which provides more detailed information on debugging. This might point to a wiki page, or to resolution information in the DroneKit-LA documentation (if there are multiple causes then it may make sense to link to DroneKit-LA docs first and then on to wiki pages). The resolution information should also contain background information.

NOTE: Originally we discussed having resolution information in the docs. This may end up there, but we'll start by making sure that the information is available to the tool first.