Elastic unbounded range query (#624)

* Tidy up

fmt

remove unneccessary -> Result<()> followed by run.unwrap() in a test

* Adding support for elasticsearch-style unbounded queries

Extend the UserInputBound to include Unbounded, so we can reuse formatting and
internal query format

* Still working on elastic-style range queries

Fixes #498

Merge the elastic_range into range

Reformat to make code easier to follow, use optional() macro to return Some

* Fixed bugs

Made the range parser insensitive to whitespace between the ":" and the range.

Removed optional parsing of field.

Added a unit test for the range parser.

Derived PartialEq to compare the results of parsing as structs, instead of
strings. Found a bug with that unit test - "*}" was parsed as an
UserInputBound::Exclusive, instead of UserInputBound::Unbounded. Added an early
detection-and-return for * in the original range parser

* Correct failing test

Assume that we will use "{*" for Unbounded ranges

* Add a note in the changelog

cargo-fmt

* Moved parenthesis to a newline to make nested if-else more visible

src/query/query_parser/query_parser.rs

@@ -369,6 +369,7 @@ impl QueryParser {
         match *bound {
             UserInputBound::Inclusive(_) => Ok(Bound::Included(term)),
             UserInputBound::Exclusive(_) => Ok(Bound::Excluded(term)),
+            UserInputBound::Unbounded => Ok(Bound::Unbounded),
         }
     }