Fix some compile errors in standard library

stdlib/io.bolt

@@ -1,5 +1,5 @@
 
-mod IO {
+pub mod IO {
 
   pub type Result<T> = Either<Error, T>;
 
@@ -7,6 +7,8 @@ mod IO {
     process.stdout.write(message);
   }
 
+  pub struct File;
+
   pub trait Read {
     fn read(self, count: usize, target: Vec<u8>) -> Result<usize>;
   }

stdlib/lang/bolt.bolt

@@ -1,6 +1,9 @@
 
-import "../option"
-import "../numbers"
+import "../option";
+import "../numbers";
+import "../vec";
+import "../string";
+import "../io";
 
 mod Bolt::Lang {
 
@@ -11,9 +14,9 @@ mod Bolt::Lang {
   }
 
   pub struct Span {
-    file: File,
-    start: TextPos,
-    end: TextPos,
+    file: IO::File,
+    start: Pos,
+    end: Pos,
   }
 
   pub struct Identifier {

stdlib/lib.bolt

@@ -2,7 +2,8 @@
 pub import "./option"
 pub import "./either"
 pub import "./string"
-pub import "./math.bolt"
-pub import "./vec.bolt"
+pub import "./math"
+pub import "./vec"
+pub import "./vec"
 pub import "./lang/bolt"