Add a meta file to the encrypted repo

[chmac]

Let’s add a file to the root of the encrypted repository. The file could contain:

• A version number
  • If we change the encryption scheme in the future, we can increment this flag
• The key derivation params, see Key derivation #4
• What else?

[chmac]

We can make this file JSON format I think.

[johannes87]

What I think needs to be done:

• Implement deriveKeys so it returns a Keys object, as defined in types.ts

• In index.ts, implement encrypted::password::url scheme
  If no password is given, create password and update git remote

• Write the meta file to the repository. The file contains all the information except the password from the URL scheme to create the Keys object

• encryptedPush / encryptedFetch need to be made aware of the new URL scheme