add Currency::all() and Exchange::all() which return a vec of all variants

src/crypto.rs

@@ -198,6 +198,12 @@ macro_rules! make_currency {
                     other => Err(UnlistedCurrency(other))
                 }
             }
+
+            pub fn all() -> Vec<Self> {
+                vec![
+                    $( c!($ticker) ),*
+                ]
+            }
         }
 
         impl TryFrom<u8> for Currency {
@@ -428,6 +434,12 @@ macro_rules! make_exchange {
                     ),*
                 }
             }
+
+            pub fn all() -> Vec<Self> {
+                vec![
+                    $( e!($ticker) ),*
+                ]
+            }
         }
 
         impl TryFrom<u8> for Exchange {