Reduce emissions by 10% every year (#108)

* deprecate top balance

* stub dynamic emissions impl

* impl 90% curve

* scaffold emissions rate function

* emissions curve

* implement new supply curve

* remove comments

* update comment

* bump version

* test reset

* add tests for emissions reduction

* test

* fix test

* bump version

api/src/state/config.rs

@@ -15,8 +15,8 @@ pub struct Config {
     /// The minimum accepted difficulty.
     pub min_difficulty: u64,
 
-    /// Buffer for possible future use.
-    pub _buffer: [u8; 8],
+    /// The target emissions rate in ORE/min.
+    pub target_emmissions_rate: u64,
 }
 
 account!(OreAccount, Config);