prop#001: Switch to url config option to simplify

Make executive decision that sbws.bin is better filename than the proposed
name 1G in the ticket. We can duke it out later if desired.

GH: closes #123

docs/source/proposals/001-switchtohttp.rst

@@ -119,14 +119,10 @@ Available keys in a ``[destinations.foo]`` section:
   destination should be considered unusable. (optional)
 - ``relay_section_method``: one of ``uniform_random`` or
   ``bw_weighted_random``, defaulting to whichever is a sane default (optional)
-- ``server_host``: an IPv4 address, IPv6 address, or hostname. If a hostname is
-  given, it must not be resolved once at startup; instead, it should be
-  left up to the exit relay to resolve. (required)
-- ``server_port``: a port (optional, with sane default depending on protocol)
-- ``protocol``: one of ``http`` or ``https`` (required)
-- ``file_path``: path to the resource to download from the webserver. If not
-  specified, defaults to something. It is a fatal configuration error to leave off
-  the leading ``/``. (optional)
+- ``url``: an HTTP or HTTPS URL for the bandwidth file to download. The URL's
+  hostname must not be resolved locally; instead, it should be left up to the
+  exit relay to resolve. If the URL does not contain a path, it defaults to
+  ``/sbws.bin``. (required)
 - ``weight``: when choosing between which destination to use for the next
   measurement, give this destination the specified weight. If not given,
   defaults to 100. Note how if no destinations have a weight value, they are
@@ -158,6 +154,8 @@ Example: CDN
 Relays are not specified because we want to choose from all exits in the
 network.
 
+This CDN provides ``/sbws.bin`` so we are allowed to leave off the file part.
+
 HTTPS for the protocol, and no further HTTPS options because this CDN has a
 widely-trusted certificate and doesn't care about only allowing our sbws
 scanners to download files.
@@ -165,8 +163,8 @@ scanners to download files.
 ::
 
     [destinations.cloudflare]
-    server_host = sbwsrocks.cdn.cloudflare.com
-    protocol = https
+    url = https://sbwsrocks.cdn.cloudflare.com/
+
 
 Example: Private Local Destination
 '''''''''''''''''''''''''''''''''''
@@ -191,9 +189,7 @@ entirely.
     [destionations.secure_bwauth]
     relays = AAAA...AAAA, BBBB...BBBB
     relay_section_method = uniform_random
-    server_host = 33.33.33.33
-    server_port = 4433
-    protocol = https
+    url = https://33.33.33.33:4433/sbws.bin
     client_cert = ${paths:sbws_home}/secure_bwauth_client.cert
     verify_server_cert = off
 
@@ -214,6 +210,4 @@ and add it to the config.
 ::
 
     [destination.unsuspecting_linux]
-    server_host = mirror-rotation.exaplelinux.net
-    protocol = http
-    file_path = /archive/isos/1.2.3/examplelinux-amd64-gnome-destkop.iso
+    url = http://examplelinux.net/archive/isos/1.2.3/examplelinux-amd64-gnome-destkop.iso