Arch linux support

[TellowKrinkle]

Adds support for the Arduino IDE available from the arduino and arduino-avr-core arch linux repositories. All examples now compile assuming you've installed the required Arduino libraries and set AUTO_SET_SKETCHBOOK_PATH=ON.

Hopefully fixes #53 (for Arch Linux, Ubuntu ships an ancient version 1.0.5 of the IDE, untested on Fedora)

AFAIK Fedora does something similar to Arch but I haven't tested that yet so if someone with Fedora could test that would be great

Major differences between Arch install and the default distribution:

• Binaries are installed to /usr/bin instead of a subdirectory of /usr/share/arduino
• avrdude.conf is in /etc instead of a subdirectory of /usr/share/arduino
  • I didn't see any other use of ARDUINO_SDK_ROOT_PATH so I just set that to / if this is the case. It didn't break my compiling of the examples, but if you do think that could break anything important please say so
• There is no /usr/share/arduino/libraries, all Arduino base libraries (like Stepper) are installed from the Arduino GUI package manager and get put in the user's sketchbook libraries folder.
  • If you need these, you'll need to enable AUTO_SET_SKETCHBOOK_PATH=ON or supply a sketchbook path

Other Changes

• The Arduino IDE preferences file location is in ~/.arduino15 on linux and ~/Library/Arduino15 on mac. Not sure what the old path was to, but I left it in as a fallback if the above paths don't exist
• Switched the CMAKE_HOST_ARCHLINUX AND ${USE_ARCHLINUX_BUILTIN_SUPPORT} check with a check for the existence of ${ARDUINO_SDK_PATH}/hardware/archlinux-arduino. The above check wasn't working for me, and if your arduino folder contains an archlinux-arduino subdirectory I would be surprised if that wasn't what you were supposed to use.

[TellowKrinkle]

Now tested on Fedora as well

[TellowKrinkle]

Does that seem right?