Add option main file & ignoreinitial

[indaam]

• main option to only render main file on watch
• ignoreinitial option to skip first rendered on watch

[ci-reporter]

The build is failing

✨ Good work on this PR so far! ✨ Unfortunately, the Travis CI build is failing as of 821ef34. Here's the output:

npm test

> pug-cli@1.0.0-alpha6 test /home/travis/build/pugjs/pug-cli
> mocha -R spec --bail


/home/travis/build/pugjs/pug-cli/node_modules/mocha/bin/mocha:13
const {deprecate} = require('../lib/utils');
^^^^^
SyntaxError: Use of const in strict mode.
    at Module._compile (module.js:439:25)
    at Object.Module._extensions..js (module.js:474:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:312:12)
    at Function.Module.runMain (module.js:497:10)
    at startup (node.js:119:16)
    at node.js:945:3

I'm sure you can fix it! If you need help, don't hesitate to ask a maintainer of the project!

---

Failed build for 3c78cde

npm test

> pug-cli@1.0.0-alpha6 test /home/travis/build/pugjs/pug-cli
> mocha -R spec --bail


/home/travis/build/pugjs/pug-cli/node_modules/mocha/bin/mocha:13
const {deprecate} = require('../lib/utils');
^^^^^
SyntaxError: Use of const in strict mode.
    at Module._compile (module.js:439:25)
    at Object.Module._extensions..js (module.js:474:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:312:12)
    at Function.Module.runMain (module.js:497:10)
    at startup (node.js:119:16)
    at node.js:945:3

Failed build for 7b5ab94

npm test

> pug-cli@1.0.0-alpha6 test /home/travis/build/pugjs/pug-cli
> mocha -R spec --bail


/home/travis/build/pugjs/pug-cli/node_modules/mocha/bin/mocha:13
const {deprecate} = require('../lib/utils');
^^^^^
SyntaxError: Use of const in strict mode.
    at Module._compile (module.js:439:25)
    at Object.Module._extensions..js (module.js:474:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:312:12)
    at Function.Module.runMain (module.js:497:10)
    at startup (node.js:119:16)
    at node.js:945:3

---

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