Add new getParser public API

[revin]

Here's a speculative change that adds a new public API:

getParser([options])

Returns a marky-markdown-flavored markdown-it parser object. You can attach other markdown-it plugins, inspect the internals for debugging, etc... For example:

var marky = require('marky-markdown')
var someMarkdownItPlugin = require('some-fake-markdown-it-plugin')

var parser = marky.getParser({ package: somePackage, highlightSyntax: false })

parser.use(someMarkdownItPlugin)

var html = parser.render(html)

marky.getParser(options).render(markdown) is the exact same thing as the existing marky.render(markdown, options)

[revin]

The main reason I'm proposing this is that I'm working on a live in-browser marky testing app, and having access to the parser made it possible to get access to the markdown-it token stream so I could do a Debug view. It also ends up addressing #247, which is nice.

If everybody likes this change, I can update the documentation and add some tests.

[ashleygwilliams]

what does PackageDescription mean here? feel like we may soon be removing this when we get rid of packagize.js with #282

otherwise this is a misleading name. shouldn't affect this PR, but we should change that if it means the full README

[revin]

That's the name this method has had since before I started working on marky; last I saw many months ago, the npm web site was using it for rendering package.json description fields into HTML for use in on package pages.

If they're not using it anymore, I'd be in favor of deprecating/removing it. People will be able to do basically the same thing by calling marky.getParser().renderInline(markdownSnippet), but honestly it wouldn't surprise me if nobody at all is using it anyway.

[revin]

oh yeah, and this has absolutely nothing to do with the packagize stuff!

and finally, the only reason it shows up in the diff here is because I moved it up earlier in the file so it grouped the module exports together 😕

yay legacy

[ashleygwilliams]

haha ok cool so- i think this looks awesome and i'm really excited about it. gonna add getting rid of that package description thing to #282 since we (cc/ @jefflembeck @aredridel ) are planning on getting rid of that pesky readme + desc weirdness anyways

omg 10.0.0 is gonna be so good

[ashleygwilliams]

ok! travis is FINALLY green lol. mergin'