Implement Update

[bitfield]

Currently you can create and delete a monitor, but not edit one. An Update method would allow you to change the attributes of an existing monitor.

This would be a very useful feature for the (Terraform provider)[github.com/bitfield/terraform-provider-uptimerobot], for example, which currently can only modify monitors by deleting and recreating them.

[jkotiuk]

It would be very useful if EnsurerMonitor method could modify AlertContacts information. Currently I have to remove monitor and add new one with updated contacts.

[bitfield]

I think you really want Update instead, don't you? EnsureMonitor basically exists only to add a new monitor if it doesn't already exist, not to modify existing monitors–that's what Update would do if we had it, which we should!