Feature request: support absolute (mod relative) paths in Include

[jakobharder]

Relative paths are great and have their use cases, but I also started to have some main assets.xml that merely collect "sub-mods" and it would be great if I can get rid of the ../../../.

Current:

<ModOps>
  <Include File="../../../../jakob/nates-windmill/assets.include.xml" />
  <Include File="../../../../jakob/fix-wind-direction/assets.include.xml" />
</ModOps>

Proposal with absolute paths:

<ModOps>
  <Include File="/data/jakob/nates-windmill/assets.include.xml" />
  <Include File="/data/jakob/fix-wind-direction/assets.include.xml" />
</ModOps>