[doc] Use consistent spelling/capitalization of names

Consistently use the following spelling for document formats,
programming languages, and names:

- Markdown
- Hjson
- JSON
- Verilog
- HTML
- GitHub
- CSS
- Python

Also avoid abbreviations:
- repo -> repository

Signed-off-by: Philipp Wagner <phw@lowrisc.org>
diff --git a/util/testplanner.py b/util/testplanner.py
index 9144eaa..b93eaf5 100755
--- a/util/testplanner.py
+++ b/util/testplanner.py
@@ -2,7 +2,7 @@
 # Copyright lowRISC contributors.
 # Licensed under the Apache License, Version 2.0, see LICENSE for details.
 # SPDX-License-Identifier: Apache-2.0
-r"""Command-line tool to parse and process testplan hjson
+r"""Command-line tool to parse and process testplan Hjson
 
 """
 import argparse
@@ -23,18 +23,18 @@
     parser.add_argument(
         'testplan',
         metavar='<hjson-file>',
-        help='input testplan file in hjson')
+        help='input testplan file (*.hjson)')
     parser.add_argument(
         '-r',
         '--regr_results',
         metavar='<hjson-file>',
-        help='input regression results file in hjson')
+        help='input regression results file (*.hjson)')
     parser.add_argument(
         '--outfile',
         '-o',
         type=argparse.FileType('w'),
         default=sys.stdout,
-        help='output html file (without css)')
+        help='output HTML file (without CSS)')
     args = parser.parse_args()
     outfile = args.outfile