make amount.ml a lib

src/dune

@@ -7,8 +7,9 @@
 (library
  (name mte)
  (wrapped false)
- (modules :standard \ mte base_32)
+ (modules :standard \ mte base_32 amount)
  (libraries
+  amount
   base_32
   ;
   include
@@ -23,13 +24,16 @@
   jsont
   cohttp))
 
-; crockford base32, as a lib to use [Base32] by accident *)
-
-(library
+(library ; crockford base32
  (name base_32)
  (modules base_32)
  (libraries base32))
 
+(library
+ (name amount)
+ (modules amount)
+ (libraries angstrom fmt zarith))
+
 (rule
  (target assets_crunch.ml)
  (deps