remove all trailing white space

this is just the result of

```
find -iname "*.[ch]pp" | xargs sed -i "s/ *$//"
find opm/parser/share/keywords -type f |  xargs sed -i "s/ *$//"
```

so if it causes conflicts with other patches, the others should get
priority. The rationale behind this patch is that some people tell
their editor to remove white space which leads to larger than
necessary patches...
Merge pull request #378 from andlaus/remove_trailing_whitespace

remove all trailing white space