Expand paths before passing to libxml2

[jimhester]

Fixes #80

[hadley]

Might be better to do this in C with R_ExpandFileName ?

[jimhester]

It looks like that is what path.expand() is doing (https://github.com/wch/r-source/blob/e5b21d0397c607883ff25cca379687b86933d730/src/main/platform.c#L1839-L1860)

[hadley]

Right, it just feels a little safer to do this in C to me.

[jimhester]

Ok it is so (1c303cc)

[hadley]

Perfect. Can you add a bullet to news too?

[codecov-io]

Current coverage is 50.00%

Merging #86 into master will not change coverage

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[jimhester]

done!