filestat input plugin

closes #929

plugins/inputs/filestat/README.md

@@ -0,0 +1,37 @@
+# filestat Input Plugin
+
+The filestat plugin gathers metrics about file existence, size, and other stats.
+
+### Configuration:
+
+```toml
+# Read stats about given file(s)
+[[inputs.filestat]]
+  ## Files to gather stats about.
+  ## These accept standard unix glob matching rules, but with the addition of
+  ## ** as a "super asterisk". See https://github.com/gobwas/glob.
+  files = ["/etc/telegraf/telegraf.conf", "/var/log/**.log"]
+  ## If true, read the entire file and calculate an md5 checksum.
+  md5 = false
+```
+
+### Measurements & Fields:
+
+- filestat
+    - exists (int, 0 | 1)
+    - size_bytes (int, bytes)
+    - md5 (optional, string)
+
+### Tags:
+
+- All measurements have the following tags:
+    - file (the path the to file, as specified in the config)
+
+### Example Output:
+
+```
+$ telegraf -config /etc/telegraf/telegraf.conf -input-filter filestat -test
+* Plugin: filestat, Collection 1
+> filestat,file=/tmp/foo/bar,host=tyrion exists=0i 1461203374493128216
+> filestat,file=/Users/sparrc/ws/telegraf.conf,host=tyrion exists=1i,size=47894i 1461203374493199335
+```