Improve CLI parsing error

[phillipj]

I've become fund of human readable and informative error messages with tips lately ;) Would you agree this has some benefits compared to the raw exception stack from JSON.parse()?

Somewhat inspired by issue #429 expecting functions to be valid JSON.

→ echo {name:'lebron'} | ./bin/mustache - test/_files/cli.mustache 
undefined:1
{name:lebron}
 ^
SyntaxError: Unexpected token n
    at Object.parse (native)
    at /mustache.js/bin/mustache:49:13

vs

→ echo {name:'lebron'} | ./bin/mustache - test/_files/cli.mustache 
Shooot, could not parse view as JSON.
Tips: functions are not valid JSON and keys / values must be surround with double quotes.

SyntaxError: Unexpected token n
    at Object.parse (native)
    at parseView (/mustache.js/bin/mustache:55:17)
    at /mustache.js/bin/mustache:49:8

[dasilvacontin]

This is awesome. Thanks @phillipj, love it! 😄