Tag v0.3.2

Tag 0.3.1

Update stats structs to support ES 2.0; Add Thread Pool stats

* Addresses prometheus-community#8
* Update README to note changes in ES 2.0
* Add stats for thread pool

Increment version to 0.2.1

Merge branch 'export_cluster-wide_node_stats' of https://github.com/d…

…an-cleinmark/elasticsearch_exporter into dan-cleinmark-export_cluster-wide_node_stats

0.1.1: Add a handful of new counters for indexing and merging

* Added `indices_indexing_index_total`
* Added `indices_indexing_index_time_in_millis`
* Added `indices_merges_total`
* Added `indices_merges_total_docs`
* Added `indices_merges_total_size_in_bytes`
* Added `indices_merges_total_time_in_millis`

Update Makefile.COMMON to newest version