Store arrays of byte ranges more efficiently

[eriksjolund]

Instead of storing byte ranges like this

message FileRegion {
   required uint64 regionOffset = 1;
   required uint64 regionSize = 2;
}

message InterestingByteRanges {
    repeated FileRegion fileRegions = 1;
}

I think we could store them like

message FileRegions {
    // A start position could define the end position of the previous entry.
    //  To define the endPosition of the last entry we would have to
    // add an extra StartPosition in the end of the array.
    repeated uint64 startPositions = 1;
}

message InterestingByteRanges {
    required FileRegions fileRegions = 1;
}

That should reduce the size of the header.