Tidy new arduino mk vars

Add CORE and FORCE_MONITOR_PORT to arduino-mk-vars.md and FORCE_MONITOR_PORT
to config print.

Arduino.mk

@@ -1059,6 +1059,12 @@ else
     $(call show_config_variable,DEVICE_PATH,[AUTODETECTED])
 endif
 
+ifndef FORCE_MONITOR_PORT
+    $(call show_config_variable,FORCE_MONITOR_PORT,[DEFAULT])
+else
+    $(call show_config_variable,FORCE_MONITOR_PORT,[USER])
+endif
+
 ifdef FORCE_MONITOR_PORT
     # Skips the DEVICE_PATH existance check.
     get_monitor_port = $(DEVICE_PATH)

arduino-mk-vars.md

@@ -316,6 +316,25 @@ MONITOR_PORT = com3
 
 ----
 
+### FORCE_MONITOR_PORT
+
+**Description:**
+
+Skip the MONITOR_PORT existance check.
+
+**Example:**
+
+```Makefile
+# Enable
+FORCE_MONITOR_PORT = true
+# Disable (default)
+undefine FORCE_MONITOR_PORT
+```
+
+**Requirement:** *Optional*
+
+----
+
 ### USER_LIB_PATH
 
 **Description:**
@@ -392,6 +411,29 @@ ARDUINO_VAR_PATH = ~/sketchbook/hardware/arduino-tiny/cores/tiny
 
 ----
 
+### CORE
+
+**Description:**
+
+Name of the core *inside* the ALTERNATE_CORE or the standard core.
+
+Usually can be auto-detected as `build.core` from `boards.txt`.
+
+**Example:**
+
+```Makefile
+# standard Arduino core (undefine ALTERNATE_CORE)
+CORE = arduino
+# or
+CORE = robot
+# tiny core (ALTERNATE_CORE = arduino-tiny)
+CORE = tiny
+```
+
+**Requirement:** *Optional*
+
+----
+
 ### VARIANT
 
 **Description:**

examples/BlinkNetworkRPi/Makefile

@@ -13,7 +13,7 @@ BOARD_TAG = attiny85at8
 AVRDUDE_CONF=/usr/local/etc/avrdude.conf
 
 # Skip the monitor port existance check since it's not on our machine.
-FORCE_MONITOR_PORT=(defined)
+FORCE_MONITOR_PORT=true
 MONITOR_PORT=/dev/spidev0.0
 
 include ../../Arduino.mk