Profile picture processing

This is still single-threaded, so perf is pretty bad. Will need to think
about how to do this more efficiently in a web context where we don't
have threading.

src/error.rs

@@ -1,9 +1,10 @@
 use shatter::parser;
 
-#[derive(Eq, PartialEq, Debug)]
+#[derive(Debug)]
 pub enum Error {
     Nostr(enostr::Error),
     Shatter(parser::Error),
+    Image(image::error::ImageError),
     Generic(String),
 }
 
@@ -19,6 +20,12 @@ impl From<parser::Error> for Error {
     }
 }
 
+impl From<image::error::ImageError> for Error {
+    fn from(err: image::error::ImageError) -> Self {
+        Error::Image(err)
+    }
+}
+
 impl From<enostr::Error> for Error {
     fn from(err: enostr::Error) -> Self {
         Error::Nostr(err)