add ability to delete parsed mail

[taoxuau]

A small change for my convenience but maybe you're happy with that.

[gustawdaniel]

Great! I like mark delete but please add documentation.

[DigitalLeaves]

Hello,
First of all, thanks for this fantastic library and thanks @gustawdaniel for this addition. Very useful indeed.

Is this feature actually added and working? I tried it today and the messages remain in the inbox folder. This is my configuration:

const imap = {
  user: env.email.automation.user,
  password: env.email.automation.password,
  host: env.email.automation.host,
  port: env.email.automation.port,
  tls: true, 
  tlsOptions: { rejectUnauthorized: false },
  markDeleted: true,
  autoExpunge: true
};

However, I configured the account in an email client and the messages remain there... I see only "Seen" flag added:
flags: [ '\\Seen' ]