Support for generation of project tags file

Considering the number of project files spread in different locations
when developing an Arduino project, proper use of tags can be difficult;
resolving beyond local functions.

I've added automatic generation of a tags file, which includes:

* Standard ctags source in project dir (.c, .cpp, .h)
* Arduino source in project dir (.ide, .pde)
* Arduino core based on detected project core from Arduino install.
* Included Arduino libraries from user library folder.

As a Vim user I find this hugely useful and think it would be a useful
addtion for others. Target has been added as `make tags`.

Arduino.mk

@@ -1307,6 +1307,22 @@ $(OBJDIR)/%.sym: $(OBJDIR)/%.elf $(COMMON_DEPS)
 	@$(MKDIR) $(dir $@)
 	$(NM) --size-sort --demangle --reverse-sort --line-numbers $< > $@
 
+########################################################################
+# Ctags
+
+# Assume ctags is on path unless has been specified
+ifndef CTAGS_EXEC
+    CTAGS_EXEC = ctags
+endif
+
+# Default to 'tags' unless user has specified a tags file
+ifndef TAGS_FILE
+    TAGS_FILE = tags
+endif
+
+# ctags command: append file with user options before
+CTAGS_CMD = $(CTAGS_EXEC) $(CTAGS_OPTS) -auf
+
 ########################################################################
 # Avrdude
 
@@ -1562,6 +1578,21 @@ generate_assembly: $(OBJDIR)/$(TARGET).s
 generated_assembly: generate_assembly
 		@$(ECHO) "\"generated_assembly\" target is deprecated. Use \"generate_assembly\" target instead\n\n"
 
+.PHONY: tags
+tags:
+	rm -f $(shell pwd)/$(TAGS_FILE)
+	@$(ECHO) "Generating tags for source files: "
+	$(CTAGS_CMD) $(TAGS_FILE) $(shell find "`pwd`" -name "*.cpp" -o -name "*.h" -o -name "*.c") 
+	@$(ECHO) "Generating tags for IDO an PDE files as C++: "
+	$(CTAGS_CMD) $(TAGS_FILE) --langmap=c++:.ino --langmap=c++:.pde $(shell find "`pwd`" -name "*.ino" -o -name "*.pde")
+	@$(ECHO) "Generating tags for project libraries: "
+	$(CTAGS_CMD) $(TAGS_FILE) $(foreach lib, $(ARDUINO_LIBS),$(USER_LIB_PATH)/$(lib)/*)
+	@$(ECHO) "Generating tags for Arduino core: "
+	$(CTAGS_CMD) $(TAGS_FILE) $(ARDUINO_CORE_PATH)/*
+	@$(ECHO) "Sorting..\n"
+	@sort $(TAGS_FILE) -o $(TAGS_FILE)
+	@$(ECHO) "Tag file generation complete, output: $(TAGS_FILE)"
+
 help_vars:
 		@$(CAT) $(ARDMK_DIR)/arduino-mk-vars.md
 
@@ -1593,6 +1624,7 @@ help:
                            generated assembly of the main sketch.\n\
   make burn_bootloader   - burn bootloader and fuses\n\
   make set_fuses         - set fuses without burning bootloader\n\
+  make tags              - generate tags file including project libs and Arduino core\n\
   make help_vars         - print all variables that can be overridden\n\
   make help              - show this help\n\
 "

HISTORY.md

@@ -13,6 +13,7 @@ I tried to give credit whenever possible. If I have missed anyone, kindly add it
 - New: Add support for good old cu as monitor command (issue #492) (https://github.com/mwm)
 - Tweak: Removed tilde from documentation (issue #497). (https://github.com/sej7278)
 - New: Add a documentation how to setup Makefile for 3rd party boards (issue #499). (https://github.com/MilanV)
+- New: Add generation of tags file using ctags, which automatically includes project libs and Arduino core. (https://github.com/tuna-f1sh)
 
 ### 1.5.2 (2017-01-11)
 

arduino-mk-vars.md

@@ -11,6 +11,7 @@ The following are the different variables that can be overwritten in the user ma
 *	[Avrdude setting variables](#avrdude-setting-variables)
 *	[Bootloader variables](#bootloader-variables)
 *	[ChipKIT variables](#chipkit-variables)
+*	[Ctags variables](#ctags-variables)
 
 ## Global variables
 
@@ -1402,6 +1403,57 @@ MPIDE_DIR = $(HOME)/mpide
 
 ----
 
+## Ctags variables
+
+### TAGS_FILE
+
+**Description:**
+
+Output file name for tags. Defaults to 'tags'.
+
+**Example:**
+
+```Makefile
+TAGS_FILE = .tags
+```
+
+**Requirement:** *Optional*
+
+----
+
+### CTAGS_OPTS
+
+**Description:**
+
+Additional options to pass to `ctags` command.
+
+**Example:**
+
+```Makefile
+# Run ctags in verbose mode
+CTAGS_OPTS = -V
+```
+
+**Requirement:** *Optional*
+
+----
+
+### CTAGS_CMD
+
+**Description:**
+
+Location of `ctags` binary. Defaults to user path.
+
+**Example:**
+
+```Makefile
+CTAGS_CMD = /usr/local/bin/
+```
+
+**Requirement:** *Optional*
+
+----
+
 ### MPIDE_PREFERENCES_PATH
 
 **Description:**