Add catchall method for `sendEmail`

[damionvega]

Add a sendEmail catchall method similar to login() & sendSms():

login

Userfront.login({
  method: "password",
  email: "[email protected]",
  password: "testmodepassword",
});

sendSms

Userfront.sendSms({
  type: "securityCode",
  to: "+15558675309",
  firstFactorCode: "a9c9b41c-ce76-4f7e-915a-abf18a36a4ae",
});