Fixed compilation under MINGW64

Necessary on mingw64 2.22
Fixed test input file not found when doing out-of-source builds.
Added test for return value of QueryDoubleAttribute().
Merge pull request #108 from ddiproietto/patch-1

Fixed compilation under MINGW64
Merge pull request #109 from pzychotic/master

Fixed compiler warning for x64 build
Merge pull request #110 from pzychotic/tests

Small test addition and fix
fix floating point specifier and clean up a warning
Initialize pointers to satisfy static code analyser.