Add support for C:/paths/like/this/

[SmilyOrg]

It might be a bit out of the norm, but most tools / apps I've encountered (even cmd.exe) support forward slash style absolute paths on Windows.

If this is an explicit choice a better error message than "Path isn't absolute and no reference file provided" would be helpful at least.

I've only had a cursory look at the code, so I don't know what would be the best proper way to add this, but the simplest would be to adjust the slash direction according to expectations. I suppose modifying paths is not the most expected / preferred outcome, so perhaps adding support for both directions might be better, albeit probably trickier and would double a lot of code.

[Gama11]

Definitely seems like a bug since Windows generally supports forward slashes.

This also caused some issues for flixel-tools: HaxeFlixel/flixel-tools@01e6436

[elsassph]

I'm afraid we don't/won't have capacity to look into this issue. A fix would be appreciated.