Fix time elapsed (#1277)

* Show the actual time elapsed; add docs

* `requests.Response._headers_parsed_at` → `requests.Response._httpie_headers_parsed_at`

* Add `ELAPSED_TIME_LABEL` constant

* Tweak docs

* Tweak docs

* Allow multiple blank lines in Markdown files

* Add rudimentary tests for --meta with different --style’s

* Cleanup tests

* Cleanup tests

* Cleanup tests

docs/markdownlint.rb

@@ -20,6 +20,9 @@ exclude_rule 'MD014'
 # MD028 Blank line inside blockquote
 exclude_rule 'MD028'
 
+# MD012 Multiple consecutive blank lines
+exclude_rule 'MD012'
+
 # Tell the linter to use ordered lists:
 #   1. Foo
 #   2. Bar