CHANGELOD.md: Add note about ujson

Falcon can optionally use ujson to speed up JSON (de)serialization,
but Falcon's already really fast and requiring ujson actually makes
deployment trickier in some cases (for example in Docker containers
that are based on Alpine Linux).

Here are some tests of Falcon 1.4.1 on Python 3.5 from my laptop:

    1. falcon...............60172 req/sec or 16.62 μs/req (36x)
    2. falcon-ext...........34186 req/sec or 29.25 μs/req (20x)
    3. bottle...............32924 req/sec or 30.37 μs/req (20x)
    4. werkzeug.............11948 req/sec or 83.70 μs/req (7x)
    5. flask.................6654 req/sec or 150.30 μs/req (4x)
    6. django................4565 req/sec or 219.04 μs/req (3x)
    7. pecan.................1672 req/sec or 598.19 μs/req (1x)

The tests were conducted with Falcon's official Docker benchmarking
tools on my Intel(R) Core(TM) i7-8550U CPU @ 1.80GHz on Arch Linux.

See: https://github.com/falconry/falcon/tree/master/docker

CHANGELOG.md

@@ -4,6 +4,10 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+### [0.5.1] - 2018-10-24
+## Changed
+- Use Python's native json instead of ujson
+
 ### [0.5.0] - 2018-10-24
 ## Added
 - Example nginx configuration to README.md

indexer.py

@@ -31,7 +31,7 @@
 # See: https://wiki.duraspace.org/display/DSPACE/Solr
 
 from database import database_connection
-import ujson
+import json
 import psycopg2.extras
 from solr import solr_connection
 
@@ -56,7 +56,7 @@ def index_views():
     }, rows=0)
 
     # get total number of distinct facets (countDistinct)
-    results_totalNumFacets = ujson.loads(res.get_json())['stats']['stats_fields']['id']['countDistinct']
+    results_totalNumFacets = json.loads(res.get_json())['stats']['stats_fields']['id']['countDistinct']
 
     # divide results into "pages" (cast to int to effectively round down)
     results_per_page = 100
@@ -115,7 +115,7 @@ def index_downloads():
     }, rows=0)
 
     # get total number of distinct facets (countDistinct)
-    results_totalNumFacets = ujson.loads(res.get_json())['stats']['stats_fields']['owningItem']['countDistinct']
+    results_totalNumFacets = json.loads(res.get_json())['stats']['stats_fields']['owningItem']['countDistinct']
 
     # divide results into "pages" (cast to int to effectively round down)
     results_per_page = 100

requirements.txt

@@ -9,5 +9,4 @@ python-mimeparse==1.6.0
 requests==2.19.1
 six==1.11.0
 SolrClient==0.2.1
-ujson==1.35
 urllib3==1.23