PlatformIO Library Manager manifest file

* This library in Web: http://platformio.ikravets.com/#!/lib/show/MSP430-Energia-Xively
* Specification: [PlatformIO Library Manager](http://docs.platformio.ikravets.com/en/latest/librarymanager/index.html)
* Integration: [IDE Integration](http://docs.platformio.ikravets.com/en/latest/ide.html)

`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 "MSP430-Energia-Xively"
# Found ... libraries:
# MSP430-Energia-Xively        A library for Energia to make it easier to talk to Xively

$ platformio lib install MSP430-Energia-Xively
# Installing MSP430-Energia-Xively  library:
# Downloading  [####################################]  100%
# Unpacking  [####################################]  100%
# The library ‘MSP430-Energia-Xively' has been successfully installed!

$ platformio lib show MSP430-Energia-Xively
# MSP430-Energia-Xively
# -------------
# Author: Zack Lalanne
# Keywords: xively
# Version: ***
#
# A library for Energia to make it easier to talk to Xively

$ platformio lib update
# Updating MSP430-Energia-Xively  library:
# Versions: Current=***, Latest=***       [Up-to-date]]
```
Merge pull request #1 from ivankravets/patch-2

PlatformIO Library Manager manifest file