Returns the program/package name and version as a string with optional format customization.
npm install program-version   
> Returns the program/package name and version as a string with optional format customization.
$ npm install program-version --save
###### import and configure.
// specify directory of package.json
var version = require('program-version')(__dirname)
// directory of package.json is inferred
var version = require('program-version')()
###### program/package name, leading v and version.
version()
//=> program vN.N.N
- %(program)s: program/package name
- %(vprefix)s: v
- %(version)s: version (i.e. 0.1.0)
###### program/pacakge name only.
version('%(program)s');
//=> program
###### program/package name and version (no leading v).
version('%(program)s %(version)s');
//=> program N.N.N
###### version only.
version('%(version)s');
//=> N.N.N