[WIP] Add Evernote function

[kokufu]

Just like many people commented in #69, I also want Evernote support.
Therefore I implemented the function of synchronizing with Evernote.
Check it and let me know the next step.
It's WIP. If you find any problems, feel free to tell me or fix them.

How to run

Run on debug mode

I didn't execute gulp, so you have to run it on debug mode or execute gulp manually.

Get Evernote sandbox account

This function needs evernote-proxy.
I have launched Heroku server (free Dynos) (https://serene-forest-38715.herokuapp.com).
You can use it to check the operation.
That server is only for Evernote sandbox, so you have to create an account of sandbox at development server.

How to run on public server

When you want to test it on the public site of Evernote, you need activated API key and launch another evernote-proxy server with them.
To get API Key, go to Evernote Developers and click GET AN API KEY Button on the top right hand corner.
You can activate it at support page.

Known issues

1. To syncup, I need rendered html with stylesheet, so I use document.getElementById("preview-contents") to get it. However, the element might not finish rendering, so the uploaded page might be a little old. (Furthermore, this implementation is messy.)
2. Html to Enml converter I made is too rough. It's better to replace it by another library. (but I couldn't find one that works well on client side)
3. Title is not synced for now.
4. Icon must be made