Feat/multitab blocks

[karthik2804]

This PR also includes the refactoring of the javascript into multiple files for easier maintenance.

Shortcodes need to be enabled in the frontmatter to use multitab.

enable_shortcodes = true

The markup to create tabs in markdown is as follows

{{ tabs "Os" }}

{{ startTab "Windows"}}

To list files on windows use `dir`

<!-- @selectiveCpy -->

\`\`\`bash
$ dir hello_fermyon
\`\`\`
and script in windows have the extension `.bat`

<!-- @nocpy -->

\`\`\`bash
hello.bat
test.bat
\`\`\`

{{ blockEnd }}

{{ startTab "Linux"}}

To list files on linux use `ls`

<!-- @selectiveCpy -->

\`\`\`bash
$ ls
\`\`\`

and script in windows have the extension `.sh`

<!-- @nocpy -->

\`\`\`bash
hello.sh
test.sh
\`\`\`

{{ blockEnd }}
{{ blockEnd }}

[flynnduism]

@karthik2804 this is a great addition!

I added a separate issue #240 to raise the question of how best we could document how the formatting you outlined here (thanks for the example!) can be published for the developer who is writing & editing pages, it's not a blocker for this PR.

[mikkelhegn]

Only approving the description and example. I have not tested the code, nor read it. Consider adding a reviewer to review the JS code.

[flynnduism]

@karthik2804 I've reviewed the JS changes and it LGTM!

In package.json the task that bundles the scripts is using parcel watch > this should be parcel build to avoid those console errors on pageload. Once that's in place I think this is all good to merge.