Add configuration of text format precision

Define ASSIMP_AI_REAL_TEXT_PRECISION
8 when ai_real is float
16 when ai_real is double

code/Ply/PlyExporter.cpp

@@ -111,7 +111,7 @@ PlyExporter::PlyExporter(const char* _filename, const aiScene* pScene, bool bina
     // make sure that all formatting happens using the standard, C locale and not the user's current locale
     const std::locale& l = std::locale("C");
     mOutput.imbue(l);
-    mOutput.precision(16);
+    mOutput.precision(ASSIMP_AI_REAL_TEXT_PRECISION);
 
     unsigned int faces = 0u, vertices = 0u, components = 0u;
     for (unsigned int i = 0; i < pScene->mNumMeshes; ++i) {