Fix supporting of Windows and MacOS platforms

[PROger4ever]

In #7 we supported Windows and MacOS platforms by using platform-specific line breakers. But tests used its own variable with readyToken, so they failed. Now it is fixed.

Also I found a filename encoding problem on Windows: exiftool says file not found in stay_open mode. I fixed it by setting filename encoding explicitly.

Now go-exiftool passes its tests on Linux and Windows (I have no MacOS to test on).

[codecov-commenter]

Codecov Report

Merging #14 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #14   +/-   ##
=======================================
  Coverage   88.02%   88.02%           
=======================================
  Files           2        2           
  Lines         142      142           
=======================================
  Hits          125      125           
  Misses         11       11           
  Partials        6        6           

Impacted Files	Coverage Δ
exiftool.go	77.63% <ø> (ø)

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[barasher]

Thanks for the PR @PROger4ever
After having merged your PR, I realized that it can break backward compatibilty : the default behaviour of the library changes.
So, I've added a new functionnal option to set Exiftool's -charset argument (commit cd214fc) : https://godoc.org/github.com/barasher/go-exiftool#Charset

[PROger4ever]

Thank you for the solving this issue :)
I tested my PR on Linux+Windows and didn't notice any observable change in its behavior. However, setting charset replaces its default value in fact. Does it matter for us if practical result didn't changed?

[barasher]

The results didn't changed with the data you were working on, but it might happen on somebody else's data.
I really consider that backward compatibility is really important and that we should, as much as possible, avoid any "default" behaviour change.