rename types.cr to expr.cr

I did not separate types.cr to type.cr and expr.cr because function type
requires the definition of Crisp::Expr.  They depend on each
definitions.

src/crisp/core.cr

@@ -1,7 +1,7 @@
 require "time"
 require "readline"
 
-require "./types"
+require "./expr"
 require "./error"
 require "./printer"
 require "./reader"

src/crisp/env.cr

@@ -1,4 +1,4 @@
-require "./types"
+require "./expr"
 require "./error"
 
 module Crisp

src/crisp/evaluator.cr

@@ -3,7 +3,7 @@ require "readline"
 
 require "./reader"
 require "./printer"
-require "./types"
+require "./expr"
 require "./env"
 require "./core"
 require "./error"

src/crisp/types.cr → src/crisp/expr.cr

@@ -40,14 +40,14 @@ module Crisp
 
   class Expr
     alias Func = (Array(Expr) -> Expr)
-    alias ValueExpr = Nil | Bool | Int32 | String | Symbol | List | Vector | HashMap | Func | Closure | Atom
+    alias Type = Nil | Bool | Int32 | String | Symbol | List | Vector | HashMap | Func | Closure | Atom
 
     is_macro :: Bool
     meta :: Expr
 
     property :is_macro, :meta
 
-    def initialize(@val : ValueExpr)
+    def initialize(@val : Type)
       @is_macro = false
       @meta = nil
     end

src/crisp/interpreter.cr

@@ -3,7 +3,7 @@ require "readline"
 
 require "./reader"
 require "./printer"
-require "./types"
+require "./expr"
 require "./env"
 require "./core"
 require "./error"

src/crisp/printer.cr

@@ -1,4 +1,4 @@
-require "./types"
+require "./expr"
 
 module Crisp
   class Printer

src/crisp/reader.cr

@@ -1,4 +1,4 @@
-require "./types"
+require "./expr"
 require "./error"
 
 module Crisp