Refactor Package structure

This commit cleans up the package structure, to make two new top-level
packages `internal` (for internal-use packages) and `pkg` (for general
shared utility code).

pkg/logging/log.go

@@ -0,0 +1,30 @@
+package logging
+
+import (
+	"strings"
+
+	"github.com/tkw1536/goprogram/stream"
+)
+
+// LogOperation logs a message that is displayed to the user, and then increases the log indent level.
+func LogOperation(operation func() error, io stream.IOStream, format string, args ...interface{}) error {
+	logOperation(io, getIndent(io), format, args...)
+	incIndent(io)
+	defer decIndent(io)
+
+	return operation()
+}
+
+// LogMessage logs a message that is displayed to the user
+func LogMessage(io stream.IOStream, format string, args ...interface{}) (int, error) {
+	return logOperation(io, getIndent(io), format, args...)
+}
+
+func logOperation(io stream.IOStream, indent int, format string, args ...interface{}) (int, error) {
+	message := "\033[1m" + strings.Repeat(" ", indent+1) + "=> " + format + "\033[0m\n"
+	if !io.StdinIsATerminal() {
+		message = " => " + format
+	}
+
+	return io.Printf(message, args...)
+}