Documentation improvements

- fully document aggregator and processor plugins
- improve readme.md

closes #1989

plugins/aggregators/minmax/README.md

@@ -0,0 +1,42 @@
+# MinMax Aggregator Plugin
+
+The minmax aggregator plugin aggregates min & max values of each field it sees,
+emitting the aggrate every `period` seconds.
+
+### Configuration:
+
+```toml
+# Keep the aggregate min/max of each metric passing through.
+[[aggregators.minmax]]
+  ## General Aggregator Arguments:
+  ## The period on which to flush & clear the aggregator.
+  period = "30s"
+  ## If true, the original metric will be dropped by the
+  ## aggregator and will not get sent to the output plugins.
+  drop_original = false
+```
+
+### Measurements & Fields:
+
+- measurement1
+    - field1_max
+    - field1_min
+
+### Tags:
+
+No tags are applied by this aggregator.
+
+### Example Output:
+
+```
+$ telegraf --config telegraf.conf --quiet
+system,host=tars load1=1.72 1475583980000000000
+system,host=tars load1=1.6 1475583990000000000
+system,host=tars load1=1.66 1475584000000000000
+system,host=tars load1=1.63 1475584010000000000
+system,host=tars load1_max=1.72,load1_min=1.6 1475584010000000000
+system,host=tars load1=1.46 1475584020000000000
+system,host=tars load1=1.39 1475584030000000000
+system,host=tars load1=1.41 1475584040000000000
+system,host=tars load1_max=1.46,load1_min=1.39 1475584040000000000
+```

plugins/processors/printer/README.md

@@ -0,0 +1,14 @@
+# Printer Processor Plugin
+
+The printer processor plugin simple prints every metric passing through it.
+
+### Configuration:
+
+```toml
+# Print all metrics that pass through this filter.
+[[processors.printer]]
+```
+
+### Tags:
+
+No tags are applied by this processor.