Move to a modules/probers model, like the blackbox_exporter.

[ribbybibby]

There are a number of reasons for this change:

• Modules allow a single instance of the exporter to be configured with numerous different tls configs. Previously you had to run a different exporter for each combination.
• Adding new and more complicated options to the exporter should be easier with modules than if I was to go down the route of accepting configuration directly through url params
• I prefer defining a specific prober (https,tcp) over using the URL to guess what the user wants