[2.0.0] (WIP) Migration to NextJS&Fumadocs

[vplend]

Major changes:

• Now using .mdx instead of .md
• Include the code <include>/path/to/file#region</include>
• Code tabs

<Tabs items={['ru_ru', 'en_us']}>
  <Tab value="ru_ru"><include><include>/path/to/file</include></include></Tab>
  <Tab value="en_us"><include><include>/path/to/file</include></include></Tab>
</Tabs>

• Callouts

<Callout type="info" title="title">
  
</Callout>

<Callout type="warn" title="title">
  
</Callout>

<Callout type="error" title="title">
  
</Callout>

<Callout type="idea" title="title">
  
</Callout>