Add pluggable image readers, plus some documentation.

lib/imagereader/imagereader.cc

@@ -0,0 +1,31 @@
+#include "globals.h"
+#include "image.h"
+#include "flags.h"
+#include "dataspec.h"
+#include "sector.h"
+#include "sectorset.h"
+#include "imagereader/imagereader.h"
+#include "fmt/format.h"
+
+static bool ends_with(const std::string& value, const std::string& ending)
+{
+    if (ending.size() > value.size())
+        return false;
+    return std::equal(ending.rbegin(), ending.rend(), value.rbegin());
+}
+
+std::unique_ptr<ImageReader> ImageReader::create(const ImageSpec& spec)
+{
+    const auto& filename = spec.filename;
+
+    if (ends_with(filename, ".img") || ends_with(filename, ".adf"))
+        return createImgImageReader(spec);
+
+    Error() << "unrecognised image filename extension";
+    return std::unique_ptr<ImageReader>();
+}
+
+ImageReader::ImageReader(const ImageSpec& spec):
+    spec(spec)
+{}
+