Resolve symbolic links for all input files

[jFransham]

Closes #256.

Question: is this the right place to do this? This gives paths an IO/filesystem dependency that it didn't already have, which makes this function impure when you might expect it to return the same thing each time.

[BurntSushi]

Sorry for the late reply! Unfortunately, this bug is a bit more complex to fix. Canonicalizing all of the paths like this is a non-starter, since the output will use all of the canonicalized paths instead of their logical paths. The right solution here is to read file paths given at the command line as if they were normal files, which required fixing the underlying recursive directory iterators. For example, see: BurntSushi/walkdir#15

I'll be pushing a fix soon!