PlatformIO-based manifest file

Web: http://platformio.ikravets.com/#!/lib/show/i2cdevlib-Arduino-AK8975
Docs: http://docs.platformio.ikravets.com/en/latest/librarymanager/index.html
Avoid trademark issues with library name
Correct keywords
Add MPU6050 dependency
Merge pull request #90 from ivankravets/patch-2

PlatformIO Library Manager manifest file