Read input regardless of whether or not it's a TTY

This commit also contains some refactors:

* Refactor away inputStatus type
* Refactor away program.inputIsTTY member
* Simplify how we setup and restore input when it's a TTY

tty_unix.go

@@ -3,7 +3,6 @@
 package tea
 
 import (
-	"errors"
 	"io"
 	"os"
 
@@ -11,39 +10,25 @@ import (
 )
 
 func (p *Program) initInput() error {
-	if !p.inputIsTTY {
-		return nil
+	// If input's a file, use console to manage it
+	if f, ok := p.input.(*os.File); ok {
+		c, err := console.ConsoleFromFile(f)
+		if err != nil {
+			return nil
+		}
+		p.console = c
 	}
 
-	// If input's a TTY this should always succeed.
-	f, ok := p.input.(*os.File)
-	if !ok {
-		return errInputIsNotAFile
-	}
-
-	c, err := console.ConsoleFromFile(f)
-	if err != nil {
-		return nil
-	}
-	p.console = c
-
 	return nil
 }
 
 // On unix systems, RestoreInput closes any TTYs we opened for input. Note that
-// we don't do this on Windows as it causes the prompt to not be drawn until the
-// terminal receives a keypress rather than appearing promptly after the program
-// exits.
+// we don't do this on Windows as it causes the prompt to not be drawn until
+// the terminal receives a keypress rather than appearing promptly after the
+// program exits.
 func (p *Program) restoreInput() error {
-	if p.inputStatus == managedInput {
-		f, ok := p.input.(*os.File)
-		if !ok {
-			return errors.New("could not close input")
-		}
-		err := f.Close()
-		if err != nil {
-			return err
-		}
+	if p.console != nil {
+		return p.console.Close()
 	}
 	return nil
 }