allow both 1.5 and 1.0 Arduino library format

[ianfixes]

We'll need to be able to handle library / header files that are both in the root project directory (Arduino 1.0) and in the src/ directory (Arduino 1.5).

https://github.com/arduino/arduino/wiki/arduino-ide-1.5:-library-specification

[ianfixes]

I find all the CPP files from the root directory of the library, so this should be irrelevant. Should.