Provide data from last API version on a non-versioned path

[rafaellehmkuhl]

Since t0.11.15 the API has broken compatibility with older versions, as now the API version needs to be included in the route path (/v1 in the path beggining).

This change breaks applications that are using mavlink2rest, forcing them to not upgrade or to put a routine to check the mavlink2rest version that it's being consumed and deal with that (putting the /v1 for the newer version).

My suggestion would be for mavlink2rest to work on non-versioned paths (today it gives a "404") and deliver the latest API version for those cases. This would prevent applications from breaking and at the same time allowing access to the versioned route.

[rafaellehmkuhl]

Fixed with #88