builtin: document the basic types

The recursive definitions are illegal Go, but godoc doesn't mind.

R=bradfitz, r, n13m3y3r, rsc
CC=golang-dev
https://golang.org/cl/5322067

src/pkg/builtin/builtin.go

@@ -10,6 +10,82 @@
 */
 package builtin
 
+// bool is the set of boolean values, true and false.
+type bool bool
+
+// uint8 is the set of all unsigned  8-bit integers.
+// Range: 0 through 255.
+type uint8 uint8
+
+// uint16 is the set of all unsigned 16-bit integers.
+// Range: 0 through 65535.
+type uint16 uint16
+
+// uint32 is the set of all unsigned 32-bit integers.
+// Range: 0 through 4294967295.
+type uint32 uint32
+
+// uint64 is the set of all unsigned 64-bit integers.
+// Range: 0 through 18446744073709551615.
+type uint64 uint64
+
+// int8 is the set of all signed  8-bit integers.
+// Range: -128 through 127.
+type int8 int8
+
+// int16 is the set of all signed 16-bit integers.
+// Range: -32768 through 32767.
+type int16 int16
+
+// int32 is the set of all signed 32-bit integers.
+// Range: -2147483648 through 2147483647.
+type int32 int32
+
+// int64 is the set of all signed 64-bit integers.
+// Range: -9223372036854775808 through 9223372036854775807.
+type int64 int64
+
+// float32 is the set of all IEEE-754 32-bit floating-point numbers.
+type float32 float32
+
+// float64 is the set of all IEEE-754 64-bit floating-point numbers.
+type float64 float64
+
+// complex64 is the set of all complex numbers with float32 real and
+// imaginary parts.
+type complex64 complex64
+
+// complex128 is the set of all complex numbers with float64 real and
+// imaginary parts.
+type complex128 complex128
+
+// string is the set of all strings of 8-bit bytes, conventionally but not
+// necessarily representing UTF-8-encoded text. A string may be empty, but
+// not nil. Values of string type are immutable.
+type string string
+
+// int is a signed integer type that is at least 32 bits in size. It is a
+// distinct type, however, and not an alias for, say, int32.
+type int int
+
+// uint is an unsigned integer type that is at least 32 bits in size. It is a
+// distinct type, however, and not an alias for, say, uint32.
+type uint uint
+
+// uintptr is an integer type that is large enough to hold the bit pattern of
+// any pointer.
+type uintptr uintptr
+
+// byte is an alias for uint8 and is equivalent to uint8 in all ways. It is
+// used, by convention, to distinguish byte values from 8-bit unsigned
+// integer values.
+type byte byte
+
+// rune is an alias for int and is equivalent to int in all ways. It is
+// used, by convention, to distinguish character values from integer values.
+// In a future version of Go, it will change to an alias of int32.
+type rune rune
+
 // Type is here for the purposes of documentation only. It is a stand-in
 // for any Go type, but represents the same type for any given function
 // invocation.
@@ -21,11 +97,11 @@ type IntegerType int
 
 // FloatType is here for the purposes of documentation only. It is a stand-in
 // for either float type: float32 or float64.
-type FloatType int
+type FloatType float32
 
 // ComplexType is here for the purposes of documentation only. It is a
 // stand-in for either complex type: complex64 or complex128.
-type ComplexType int
+type ComplexType complex64
 
 // The append built-in function appends elements to the end of a slice. If
 // it has sufficient capacity, the destination is resliced to accommodate the