With the warning that I don't often do boards (and thus you would be best to get one of the other folks here to look this over) here is how I would change your board and why:
MRK1000 6_20_17_peters Main board.fzz (60.9 KB)
1) remove the 1 pin connectors on the jumpers as redundant.
2) Set the grid size to .025 from .1 for more room
3) straighten jumper4 for neatness.
4) Move the CPU end of jumper4 up a bit to clear the cpu more easily (because I can)
5) Reroute jumper2 so it is straight
6) reroute jumper3 so it is straight
7) make the future now by connecting the future jack live pin to unused i/o pin A4 which can be either analog or digital depending on software. Now a future sensor is a software change.
8) boost the trace size on ground to 48 mil (because we have room and bigger is better, we want the resistance in the power path to be as low as possible).
9) boost +5V and 3.3V to 48mil
10) Add bypass capacitors to the power leads, typically a .1UF ceramic and 10UF tantalum (polarized) to insure stable power.
DRC fails as it doesn't like the 2 traces overlapping the copper on the unused pad on the stereo jacks. As long as you are sure nothing connects to those pads, this should be able to be ignored. If you have constraints you can ignore any or all of these suggestions.