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, 48 insertions, 0 deletions

diff --git a/docs/source/lang/api/abs.rst b/docs/source/lang/api/abs.rst
new file mode 100644
index 0000000..d9f1ca3
--- /dev/null
+++ b/docs/source/lang/api/abs.rst
@@ -0,0 +1,48 @@
+.. highlight:: cpp
+
+.. _lang-abs:
+
+
+abs()
+======
+
+(Macro) computes the absolute value of a number.
+
+Syntax
+------
+
+::
+
+   abs(x)
+
+Parameters
+----------
+
+**x**: the number.
+
+Returns
+-------
+
+**x**: if **x** is greater than or equal to 0.
+
+**-x**: if **x** is less than 0.
+
+Warning
+-------
+
+Because of the way ``abs()`` is implemented, avoid using other
+functions or causing side effects inside the parentheses, as it may
+lead to incorrect results::
+
+    abs(a++);   // avoid this - yields incorrect results
+
+    abs(a);       // use this instead -
+    a++;          // keep other operations outside abs()
+
+
+Arduino Compatibility
+---------------------
+
+Maple's implementation of ``abs()`` is compatible with Arduino.
+
+.. include:: /arduino-cc-attribution.txt