Add appdata.xml file

This file can be shipped in Linux packages and allows the Gnome
application browser to show some additional metadata.
Merge pull request #1730 from matthijskooijman/ide-1.5.x-appdata

Add appdata.xml file
Removed redefinitions of SERIAL_* in Yun variant
Changed pins definition in variants from constants to #defines.
Merge branch 'pins-define' into ide-1.5.x
Changed pins definition in variants from constants to #defines.
Merge branch 'master' of github.com:arduino/Arduino
[sam] Fixed wrap-around bug in delay() (Mark Tillotson)

Fixes #1736
[sam] Fixed regression in analogRead() (fails to read multiple channels)

Fixes #1740
[sam] Fixed regression in analogRead() (fails to read multiple channels) (Mark Tillotson)

See #1740 #1634

http://forum.arduino.cc/index.php?topic=203322.msg1509907#msg1509907
Introducing "defaultTarget" board is the one selected in preferences is not available. Closes #1731
Print.print optimization. Closes #1760
Optimized Print::print(String&) (part 2)
Add Print::write(const char *, size_t)

The new function just calls Print::write(const uint8_t *, size_t), but
this allows writing out a buffer of chars (without having to learn about
casts).
Add uint8_t* versions of methods in Stream

The new functions just call their char* equivalents, but this allows
reading bytes into a buffer of uint8_t as well as chars.
Remove unneeded casts in Print::write(const String&)

Now that Print::write(const char*) is also available, these casts are no
longer needed.
Implemented support for 1.5 libraries specification rev.2

- removed "arch" folder support
- allow to optinally use "src" folder
- slightly changed metadata

For more information see:
https://github.com/arduino/Arduino/wiki/Arduino-IDE-1.5:-Library-specification
http://goo.gl/gfFJzU
Added a warning for library using the no longer supported "arch" folder
Use Files instead of String to handle paths in Compiler class.
IDE do not hide libraries with incompatible architectures