PlatformIO Library Manager manifest file

* This library in Web: http://platformio.ikravets.com/#!/lib/show/ARM-Energia-SD
* PlatformIO Library Manager: http://docs.platformio.ikravets.com/en/latest/librarymanager/index.html
* Energia IDE: [Integration of PlatformIO library manager to Energia IDE](http://www.ikravets.com/computer-life/platformio/2014/10/07/integration-of-platformio-library-manager-to-arduino-and-energia-ides)

`library.json` is a library manifest file which can be used with different tools/managers to organise embedded libraries. Currently, only [PlatformIO](http://platformio.ikravets.com) uses it.  How does this look from CLI:

```bash
$ platformio lib search "sd"
# Found ... libraries:
# ARM-Energia-SD        This library aims to expose a subset of SD card functionality in the form of a higher level 'wrapper' object (adaptation for LaunchPad LM4F120 / TM4C123)

$ platformio lib install ARM-Energia-SD 
# Installing ARM-Energia-SD  library:
# Downloading  [####################################]  100%
# Unpacking  [####################################]  100%
# The library 'ARM-Energia-SD' has been successfully installed!

$ platformio lib show ARM-Energia-SD 
# ARM-Energia-SD 
# -------------
# Author: Rei Vilo
# Keywords: sd, card, file, system
# Version: ***
#
# This library aims to expose a subset of SD card functionality in the form of a higher level 'wrapper' object (adaptation for LaunchPad LM4F120 / TM4C123)

$ platformio lib update
# Updating ARM-Energia-SD  library:
# Versions: Current=***, Latest=*** 	 [Up-to-date]]
```