upgrading to 1.2 doc

UPGRADING_12.md

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+Upgrading to 1.2
+================
+
+Version 1.2 of the library includes a few large breaking changes.
+
+### AbPrinter
+
+Arduboy no longer subclasses `Print` so no more printing/text operations.  Use the new AbPrinter class instead.
+
+    // Before
+    Arduboy arduboy;
+    // ...
+    arduboy.print("Hello");
+    
+    // After
+    Arduboy arduboy;
+    // ...
+    AbPrinter text(arduboy);
+    text.print("Hello");
+
+
+### ArduboyTunes
+
+ArduboyTunes is no longer part of the library.  If you want it you can still use it.  You can find it at https://github.com/Arduboy/ArduboyPlayTune.  Look at the Tunes examples for how to use the library now that it's been split into it's own library.
+
+There are also other great choices such as [Squawk](https://github.com/stg/Squawk), etc.  Or you can now use the standard Arduino Tone library without any issues.
+
+We still recommend you use `audio.on()`, `audio.off()`, and `audio.enabled()` to manage the actual state of the audio system.
+
+
+### Frame rate
+
+The [previous frame rate logic was buggy](https://github.com/Arduboy/Arduboy/pull/115) and would cause your game to run too slow.  
+
+After upgrading your game could possibly run 50-100% faster than before.  You'll need to playtest and make sure you adjust your game timings for the new accurate framerate logic (or set a slower framerate).