Resolves #58

This PR adds basic session support. Sessions are sealed (encrypted and signed with a private key) in cookies using iron-webcrypto (thanks @brc-dd ❤️) and uncrypto to work out of with Node.js and other environments.

The encrypted session is carried over cookies, therefore no server storage is required for session support.

Multiple session support is also possible with this implementation and custom name option (default is h3 and used for cookie name as well )

Default cookie options are secure, httpOnly with path of / (can be configured)

Exposed utils:

• useSession: Initializes session and returns an { data, id, update(val), clear() } interface to manage session. Wrapping getSession, updateSession and clearSession
• getSession: Treis to reuse or otherwise init an empty session for user
• updateSession: Updates session both in cookie and context. Also initializes if not initialized yet
• clearSession: Clears session from both cookie and context

Simple usage:

import { useSession } from 'h3'

const sessionPassword = "secretsecretsecretsecretsecretsecretsecret"

export default eventHandler(async (event) => {
      const session = await useSession<{ ctr: number }>(event, { password: sessionPassword });
      await session.update((data) => ({ ctr: Number(data.ctr || 0) + 2 }));
      await session.update({ ctr: Number(session.data.ctr || 0) - 1 });
      return `Hello! You visited this page ${session.data.ctr} times. session id: ${session.id})`;
})

Known issues:

• each updates appends a new cookie. fixing in second PR (~> fix(setCookie): override existing set-cookie header with same name #316)