Improve Support for 45° (diagonal) up/down slopes for Advanced Trains mod

[srutzky]

It is not clear whether this is a bug report or feature request due to the current documentation being ambiguous regarding whether or not diagonal slopes are actually supported:

there are other limitations to advtrains slope track. Documentation TBD.

Either way, 45 degree up/down slopes do not currently support Advanced Trains diagonal sloping tracks, and they should (regardless of whether or not this is expected functionality), at least when the using Mode 2 / Advanced Trains mode.

There are actually two issues preventing Tunnelmaker (an awesome mod, btw) from supporting Advanced Trains up/down slope tracks:

1. Tunnelmaker only places a single diagonal step (up or down) when two are required by the Advanced Trains sloping track (just like with straight / 0° / orthogonal slopes).
2. Tunnelmaker places blocks to the sides of the newly created blocks. When creating multiple steps and then removing every other raised / lowered center block (what is required by the current Tunnelmaker functionality in order to get the Advanced Trains sloping track to work), the blocks that had been placed to the sides of every raised / lowered step cut into the Advanced Trains sloping track). This is not just an aesthetic problem; it also causes trains riding on tracks to stop and is not passable).

Hopefully the attached images will further explain both issues:

• Below you can see that Tunnelmaker, when digging a diagonal down slope, places a single block / step at the corner of the clicked-on block / step. However, Advanced Trains will not allow you to add a sloping track to this setup. It will error saying, "Can't place: There's no slope of length 1".
  

• Below you can see that digging every other diagonal step up/down will provide the 2 blocks per level setup required by Advanced Trains sloping track, but then the slope of a lined tunnel will be off.
  

• Below you can see that the slope of the Advanced Trains diagonal sloping track cuts into the two blocks to the left and right of the center block that the diagonal sloping track is placed on. All four blocks need to be removed. In the picture, the blocks that were on the right side of the highlighted block have already been removed.
  

Now, as a workaround for the time being, you can add / remove an extra block / step (at the same level) at the corner of the one added / removed by Tunnelmaker, but that is far from ideal. Biggest issue is if the tunnel is lined (i.e. under water) then you need to remove 2 - 3 blocks at the very front / center in order to do another dig (and do it quickly before water starts coming in lest you get more glass blocks to clean up), and then no matter what there are still two columns of glass nodes to remove from the front after you do the digging.

[srutzky]

@kestral246 pointed out to me that you can alternate between sloping 45° and horizontal 45° up/down and it will work. I tried it and yes, it does. So, I will at least update the title of this to reflect that support should merely be improved (to handle this as a singular operation), but it does actually work (even if a bit clunky, especially when doing rather long slopes). And I did test with a lined tunnel under water.