elastic v0.7.0

NEW FEATURES

• New function scroll_clear() to clear search contexts created when
  using scroll() (#140)
• New function ping() to ping an Elasticsearch server to see if
  it is up (#138)
• connect() gains new parameter es_path to specify a context path,
  e.g., the bar in http://foo.com/bar (#137)

MINOR IMPROVEMENTS

• Change all httr::content() calls to parse to plain text
  and UTF-8 encoding (#118)
• Added note to docs that when using scroll() all scores are
  zero b/c scores are not calculated/tracked (#127)
• connect() no longer pings the ES server when run, but can
  now be done separately with ping() (#139)
• Let http request headers be sent with all requests - set with
  connect() (#129)
• Added transport_schema param to connect() to specify
  http or https (#130)
• By default use UUIDs with bulk API with docs_bulk() (#125)

BUG FIXES

• Fix to fail well on empty body sent by user (#119)
• Fix to docs_bulk() function so that user supplied doc_ids
  are not changed at all now (#123)