Theming of entire workbench

[pahen]

This PR adds the script npm run build to automatically generate the 3 themes from the colors schemes defined in https://github.com/ayu-theme/ayu-colors.

This is tested with the latest Code Insiders. It should work with 1.12 too but with some elements not styled correctly.

I removed the italic styling on comments in the editor since there's currently no way to disable that in vscode and fonts are really hard to read in italic (like Operator Mono).

I also renamed the name of the package from "ayu" to "vscode-ayu" since I couldn't install "ayu" from NPM due to conflicting name in package.json.

There's still things I feel missing in the theme but there's currently no support for styling everything in the theming API yet. But I'll suggest we'll wait with that and create a roadmap and add that when/if the support is added. Here's some of the things I would like to fix:

• Add left border to sidebar - Theming: introduce border colors for individual components to override contrastBorder microsoft/vscode#26530
• Themeing for editor squiggles - Themeing for editor squiggles background microsoft/vscode#16204 + Change the colour of warning/error squiggles microsoft/vscode#9819
• Feature request: bold_folder_labels setting like Sublime's -
  Feature request: bold_folder_labels setting like Sublime's microsoft/vscode#10748
• Hide sidebar's Tree View/Explorer arrows - [icon themes] Hide sidebar's Tree View/Explorer arrows microsoft/vscode#25655

Install the VSIX here: https://www.dropbox.com/s/eyg6l692fd73fju/vscode-ayu-0.3.0.vsix?dl=1

Fixes #7
Fixes #3

Light

Dark

Mirage

[teabyii]

Nice, I will check it later.

[pahen]

I updated terminal colors to use same colors as https://github.com/ayu-theme/ayu-vim/tree/master/term. It uses better colors for the light theme.

[teabyii]

@pahen I reverted the package name to "ayu" because I could not update the extention name in vscode market. I didn't want to publish a new one, so. And we can install package ayu by npm install when ayu in devDependencies. It's just like a trick.😃