Implement plain view

This implements a way to access plain blobs by path (similar to the
tree view) instead of by sha1.

Signed-off-by: Lars Hjemli <hjemli@gmail.com>

ui-plain.h

@@ -0,0 +1,6 @@
+#ifndef UI_PLAIN_H
+#define UI_PLAIN_H
+
+extern void cgit_print_plain(struct cgit_context *ctx);
+
+#endif /* UI_PLAIN_H */