Overhaul config <-> agent coupling. Put config in it's own package.

internal/config/testdata/subconfig/exec.conf

@@ -0,0 +1,8 @@
+[[plugins.exec]]
+  # specify commands via an array of tables
+  [[plugins.exec.commands]]
+  # the command to run
+  command = "/usr/bin/myothercollector --foo=bar"
+
+  # name of the command (used as a prefix for measurements)
+  name = "myothercollector"

internal/config/testdata/subconfig/memcached.conf

@@ -0,0 +1,9 @@
+[[plugins.memcached]]
+  servers = ["192.168.1.1"]
+  pass = ["some", "strings"]
+  drop = ["other", "stuff"]
+  interval = "5s"
+  [plugins.memcached.tagpass]
+    goodtag = ["mytag"]
+  [plugins.memcached.tagdrop]
+    badtag = ["othertag"]

internal/config/testdata/subconfig/procstat.conf

@@ -0,0 +1,5 @@
+[[plugins.procstat]]
+  [[plugins.procstat.specifications]]
+  pid_file = "/var/run/grafana-server.pid"
+  [[plugins.procstat.specifications]]
+  pid_file = "/var/run/influxdb/influxd.pid"