added support for Distribution metrics

Author: Brian Lomeland

README.md

@@ -60,6 +60,9 @@ meter(stat, value, tags)
 
 -- Sets
 meter(stat, value, tags)
+
+-- Distribution
+distribution(stat, value, tags)
 ```
 Sample rates are your responsiblity to calculate.  If you tell it the sample rate is 0.10 (10 percent), then the **value** you send needs to be the sampled value.  e.g. If you've had 100 hits and you send a 0.20 sample rate, the value you send would be 20
 

lib/ngx_lua_datadog.lua

@@ -83,5 +83,8 @@ function dogstatsd_mt:set(stat, value, tags)
   return self:send_dogstatsd(stat, value, "s", nil, tags)
 end
 
-return dogstatsd_mt
+function dogstatsd_mt:distribution(stat, value, tags)
+  return self:send_dogstatsd(stat, value, "d", nil, tags)
+end
 
+return dogstatsd_mt