PICout improvement:

* renamed private members for more clear code
 * registerExternalBufferID() method to obtain unique ID for withExternalBuffer()
 * PICoutManipulators::PICoutStdStream enum for select stream (stdout or stderr)
 * Constructors now accept optional stream
 * piCerr and piCerrObj macros

PIDir::temporary() moved to "mkdtemp"

PILog:
 * now 4 levels
 * you can set max level
 * Error writes to piCerr

libs/main/io_devices/pidir.cpp

@@ -459,7 +459,7 @@ PIDir PIDir::current() {
 
 PIDir PIDir::home() {
 #ifndef ESP_PLATFORM
-	char * rc = 0;
+	char * rc = nullptr;
 #endif
 #ifdef WINDOWS
 	rc = new char[1024];
@@ -482,7 +482,7 @@ PIDir PIDir::home() {
 #else
 #  ifndef ESP_PLATFORM
 	rc = getenv("HOME");
-	if (rc == 0) return PIDir();
+	if (!rc) return PIDir();
 	return PIDir(rc);
 #  else
 	return PIDir();
@@ -492,7 +492,7 @@ PIDir PIDir::home() {
 
 
 PIDir PIDir::temporary() {
-	char * rc = 0;
+	char * rc = nullptr;
 #ifdef WINDOWS
 	rc = new char[1024];
 	memset(rc, 0, 1024);
@@ -507,8 +507,8 @@ PIDir PIDir::temporary() {
 	s.prepend(separator);
 	return PIDir(s);
 #else
-	rc = tmpnam(0);
-	if (rc == 0) return PIDir();
+	rc = mkdtemp("/tmp/pidir_tmp_XXXXXX");
+	if (!rc) return PIDir();
 	PIString s(rc);
 	return PIDir(s.left(s.findLast(PIDir::separator)));
 #endif