Fix some import errors in standard library

stdlib/io.bolt

@@ -1,4 +1,9 @@
 
+import "./numbers"
+import "./either"
+import "./vec"
+import "./string"
+
 pub mod IO {
 
   pub type Result<T> = Either<Error, T>;

stdlib/lib.bolt

@@ -4,6 +4,5 @@ pub import "./either"
 pub import "./string"
 pub import "./math"
 pub import "./vec"
-pub import "./vec"
 pub import "./lang/bolt"
 

stdlib/numbers.bolt

@@ -1,7 +1,11 @@
 
+pub struct i8;
+pub struct i16;
 pub struct i32;
 pub struct i64;
 pub struct isize;
+pub struct u8;
+pub struct u16;
 pub struct u32;
 pub struct u64;
 pub struct usize;