Add rename processor (#4528)

plugins/processors/rename/README.md

@@ -0,0 +1,41 @@
+# Rename Processor Plugin
+
+The `rename` processor renames measurements, fields, and tags.
+
+### Configuration:
+
+```toml
+## Measurement, tag, and field renamings are stored in separate sub-tables.
+## Specify one sub-table per rename operation.
+[[processors.rename]]
+[[processors.rename.measurement]]
+  ## measurement to change
+  from = "network_interface_throughput"
+  to = "throughput"
+
+[[processors.rename.tag]]
+  ## tag to change
+  from = "hostname"
+  to = "host"
+
+[[processors.rename.field]]
+  ## field to change
+  from = "lower"
+  to = "min"
+
+[[processors.rename.field]]
+  ## field to change
+  from = "upper"
+  to = "max"
+```
+
+### Tags:
+
+No tags are applied by this processor, though it can alter them by renaming.
+
+### Example processing:
+
+```diff
+- network_interface_throughput,hostname=backend.example.com,units=kbps lower=10i,upper=1000i,mean=500i 1502489900000000000
++ throughput,host=backend.example.com,units=kbps min=10i,max=1000i,mean=500i 1502489900000000000
+```