a few more doc comments

cplusplus/include/vips/VError8.h

@@ -39,6 +39,10 @@
 
 VIPS_NAMESPACE_START
 
+/**
+ * The libvips error class. It holds a single string containing an 
+ * internationalized error message in utf-8 encoding.
+ */
 class VIPS_CPLUSPLUS_API VError : public std::exception {
 	std::string _what;
 

cplusplus/include/vips/VImage8.h

@@ -54,8 +54,9 @@ enum VSteal {
 	STEAL = 1
 };
 
-/* A smart VipsObject pointer class ... use g_object_ref()/_unref() for
- * lifetime management.
+/**
+ * A smart VipsObject pointer. It calls g_object_ref()/_unref() for you
+ * automatically.
  */
 class VObject
 {

cplusplus/include/vips/VInterpolate8.h

@@ -34,6 +34,13 @@
 
 VIPS_NAMESPACE_START
 
+/** 
+ * An interpolation. You can pass one of these to something like
+ * VImage::affine for it to use to interpolate pixels.
+ *
+ * The available interpolators vary a bit with your libvips version and how it
+ * was built, but will include `nearest`, `bilinear` and `bicubic`.
+ */
 class VInterpolate : VObject
 {
 public: