feat: add #inspect(io : IO)

spec/ulid_spec.cr

@@ -62,6 +62,15 @@ describe Ulid::ULID do
     ulid.to_s.should eq "CNK6ET39D9NPRVBEDXR72WKKEG"
   end
 
+  it "should return a custom inspect value" do
+    bytes = array_slice [
+      101, 102, 103, 104, 105, 106,
+      107, 108, 109, 110, 111, 112, 113, 114, 115, 116,
+    ] of UInt8
+    ulid = Ulid::ULID.new(bytes)
+    ulid.inspect.should eq "#<Ulid::ULID CNK6ET39D9NPRVBEDXR72WKKEG>"
+  end
+
   it "should instantiate from a string" do
     ulid = Ulid::ULID.new "CNK6ET39D9NPRVBEDXR72WKKEG"
     ulid.to_s.should eq "CNK6ET39D9NPRVBEDXR72WKKEG"

src/ulid.cr

@@ -44,8 +44,14 @@ module Ulid
       initialize(Base32.decode(str, Base32::Crockford))
     end
 
-    def to_s : String
-      Base32.encode(@bytes, Base32::Crockford)
+    def to_s(io : IO) : Void
+      io << Base32.encode(@bytes, Base32::Crockford)
+    end
+
+    def inspect(io : IO) : Void
+      io << "#<" << self.class.name << " "
+      to_s(io)
+      io << ">"
     end
 
     def time : Time