Add static code analysis with JSHint.

To eliminate frequent errors in a code it should be verified by
static analyzer. JSHint is choosen as default one due to its wide
community support. Repetitive command line launching replaced with
appropriate Grunt task. Analyzer settings defined in `.jshintrc` file.

How to launch:
 * Make sure grunt-cli is availabe on command line
 * If no - issue `sudo npm install grunt-cli -g` command
 * Type `grunt` or `grunt jshint` in terminal
 * Observe detected errors in your perfect code :)