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, 50 insertions, 0 deletions

diff --git a/docs/source/lang/cpp/const.rst b/docs/source/lang/cpp/const.rst
new file mode 100644
index 0000000..ad0c580
--- /dev/null
+++ b/docs/source/lang/cpp/const.rst
@@ -0,0 +1,50 @@
+.. highlight:: cpp
+
+.. _lang-const:
+
+``const``
+=========
+
+The ``const`` keyword stands for "constant". It is a variable
+*qualifier* that modifies the behavior of the variable, making a
+variable "*read-only*". This means that the variable can be used just
+as any other variable of its type, but its value cannot be
+changed. You will get a compiler error if you try to assign a value to
+a ``const`` variable.
+
+Constants defined with the ``const`` keyword obey the same rules of
+:ref:`variable scoping <lang-scope>` that govern other
+variables. This, and the pitfalls of using :ref:`#define
+<lang-define>`, often makes using the ``const`` keyword a superior
+method for defining constants than ``#define``.
+
+Example
+-------
+
+ ::
+
+    // this defines a variable called "pi", which cannot be changed:
+    const float pi = 3.14;
+    float x;
+
+    // ....
+
+    x = pi * 2;    // it's fine to find the value of a const variable
+
+    pi = 7;        // illegal - you can't write to (modify) a constant
+
+**#define** or **const**
+------------------------
+
+You can use either ``const`` or ``#define`` for creating numeric or
+string constants. For :ref:`arrays <lang-array>`\ , you will need
+to use ``const``. In general, ``const`` is preferred over ``#define``
+for defining constants.
+
+See Also
+--------
+
+-  :ref:`#define <lang-define>`
+-  :ref:`volatile <lang-volatile>`
+
+.. include:: /arduino-cc-attribution.txt