docs: added new API compatibility section

Signed-off-by: Mihai Tudor Panu <mihai.tudor.panu@intel.com>

README.md

@@ -114,6 +114,15 @@ API Documentation
 <a href="http://iotdk.intel.com/docs/master/upm/python"><img src="docs/icons/python.png"/></a>
 <a href="http://iotdk.intel.com/docs/master/upm/node"><img src="docs/icons/node.png"/></a>
 
+### API Compatibility
+Even if we try our best not to, every once in a while we are forced to modify
+our API in a way that will break backwards compatibility. If you find yourself
+unable to compile code that was working fine before a library update, make sure
+you check the [API changes](docs/apichanges.md) section first.
+
+**NOTE** - Our **C++ header files** will change their extension from *.h* to
+*.hpp* in the upcoming version.
+
 ### Changelog
 Version changelog [here](docs/changelog.md).
 

docs/apichanges.md

@@ -0,0 +1,20 @@
+API Changes                       {#apichanges}
+===============
+
+**IMPORTANT NOTICE**
+
+Our **C++ header files** will change their extension from *.h* to *.hpp*. This
+change is anticipated in the upcoming version and unfortunately will break
+source compatibility with previous versions of UPM for every library. You will
+need to update your code and change to the new extension format in your
+`#include` directives.
+
+Here's a list of other API changes made to the library that break source/binary
+compatibility between releases:
+
+ * **my9221**, **groveledbar** and **grovecircularled** are now all part of the
+ same library (my9221) and new functionality was added going to v.0.5.1
+ * **stepmotor** driver API was changed significantly from v.0.4.1 to v.0.5.0
+ * **eboled** library was greatly improved in version 0.4.0 and the `draw()`
+ function was removed in favor of a more complete GFX library implementation
+