merge libmaple docs ("leaflabs-docs") into ./docs

In the past, libample documentation was forked out of this repository
because the documentation had increased in scope. For the librambutan,
and the rambutan project in general, we will try to keep documentation
closer to the source code, so the librambutan-specific documentation
should live here. Other sections of leaflabs-docs will be culled in a
following commit.

This merge attempts to maintain history by using a subtree strategy.
Followed directions at:

    http://nuclearsquid.com/writings/subtree-merging-and-you/

Full history for files should be accessible using the "--follow" flag to
git log, eg:

    git log --follow docs/source/adc.rst

It should be possible to pull patches from leaflabs-docs with:

    git pull -s subtree leaflabs-docs master

... at least until the docs in this repository diverge significantly.

1 files changed, 119 insertions, 0 deletions

diff --git a/docs/source/lang/api/analogread.rst b/docs/source/lang/api/analogread.rst
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+.. highlight:: cpp
+
+.. _lang-analogread:
+
+.. _lang-api-analogread:
+
+analogRead()
+============
+
+Used to perform ADC conversion.
+
+.. contents:: Contents
+   :local:
+
+Library Documentation
+---------------------
+
+.. doxygenfunction:: analogRead
+
+Discussion
+----------
+
+Reads the value from the specified analog pin.  The Maple boards
+contain 16-channel, 12-bit analog to digital converters.  This means
+that a converter will map input voltages between 0 and 3.3 volts into
+integer values between 0 and 4095.  However, a number of factors
+interfere with getting full accuracy and precision.  For more
+information, see :ref:`adc`.
+
+Before calling analogRead() on a pin, that pin must first be
+configured for analog input, using :ref:`lang-pinMode`.  You only have
+to do this once, so it's usually done in :ref:`lang-setup`\ .
+
+Parameter Discussion
+--------------------
+
+The pin parameter is the number of the analog input pin to read from.
+The pins which support analog to digital conversion have ``AIN``
+listed underneath their number on your board's silkscreen.  These pin
+numbers are available to your program in the :ref:`boardADCPins
+<lang-board-values-adc-pins>` board-specific array.  The number of
+pins which are capable of analog to digital conversion on your board
+is given by the ``BOARD_NR_ADC_PINS`` constant.  These values are
+documented for each board in the :ref:`Board Hardware Documentation
+<index-boards>` pages.
+
+.. note:: Pin 3 is not marked ``AIN`` on the silkscreen for Maple
+   revisions through Rev 5; however **it does work** as an analog
+   input pin.
+
+Note
+----
+
+If the analog input pin is not connected to anything, the value
+returned by ``analogRead()`` will fluctuate due to a number of reasons
+(like the values of the other analog inputs, how close your hand is to
+the board, etc.) in a "random" way.
+
+Example
+-------
+
+::
+
+    int analogPin = 3;     // Potentiometer wiper (middle terminal) connected
+                           // to analog pin 3. outside leads to ground and +3.3V.
+                           // You may have to change this value if your board
+                           // cannot perform ADC conversion on pin 3.
+
+    int val = 0;           // variable to store the value read
+
+    void setup() {
+      pinMode(analogPin, INPUT_ANALOG); // set up pin for analog input
+    }
+
+    void loop() {
+      val = analogRead(analogPin);    // read the input pin
+      SerialUSB.println(val);         // print the value, for debugging with
+                                      // a serial monitor
+    }
+
+Arduino Compatibility
+---------------------
+
+The Arduino board contains a 6 channel (8 channels on the Mini and
+Nano, 16 on the Mega), 10-bit analog to digital converter with an
+input voltage range of 0V--5V. This means that it will map input
+voltages between 0 and 5 volts (which is **larger** than Maple's range
+of 0V-3.3V) into integer values between 0 and 1023 (which is
+**smaller** than the Maple's range of 0--4095).
+
+This yields a theoretical resolution between readings of: 5 volts /
+1024 units or .0049 volts (4.9 mV) per unit on Arduino boards, which
+is larger, and thus less precise, than Maple's 0.0008 volts (0.8 mV).
+
+If your program expects Arduino-style 10-bit ADC, you can :ref:`right
+shift <lang-bitshift>` the value of a Maple readout by 2, like so::
+
+    // right shift means that the result will be between 0 and 1023;
+    // be aware that you're losing a lot of precision if you do this
+    int adc_reading = analogRead(pin) >> 2;
+
+.. FIXME [0.1.0] Mention that Native can do analogReference()
+
+On the Arduino, the input range and resolution can be changed using
+the `analogReference()
+<http://arduino.cc/en/Reference/AnalogReference>`_ function. Because
+of hardware restrictions, this function is not available on the Maple
+and Maple RET6 Edition.  If your inputs lie in a different voltage
+range than 0V--3.3V, you'll need to bring them into that range before
+using ``analogRead()``.  See the :ref:`ADC reference <adc-range>` for
+more information.
+
+See Also
+--------
+
+- :ref:`ADC tutorial <adc>`
+- `(Arduino) Tutorial: Analog Input Pins <http://arduino.cc/en/Tutorial/AnalogInputPins>`_
+
+.. include:: /arduino-cc-attribution.txt