Man page fixes (#1364)

- Highlighting for options (-x, --x) now doesn't strip the prefix (may be whitespace).
- Escape sequences are now cross-platform compatible (directly taken by groff/troff [man's renderer])
- Now we check for the section before displaying the man pages.
- On MacOS, there is HTTP(n) which is different from our HTTP(1). This used to conflict with it, and we showed the wrong page. Now we specifically ask foir HTTP(1).
- Errors that might happen (e.g non executable man command) is now suppressed. So in the worst case (if anything regarding man execution goes wrong), we'll always display the manual.
- Docs for man pages.
- HTTPie man pages.
- Epilog for the man pages (see also)
- Auto-generated comments.

httpie/manager/cli.py

@@ -20,6 +20,7 @@ COMMANDS = {
             {
                 'flags': ['-f', '--format'],
                 'choices': ['json'],
+                'help': 'Format to export in.',
                 'default': 'json'
             }
         ],
@@ -166,5 +167,12 @@ parser.add_argument(
     '''
 )
 
-options = parser_to_parser_spec(parser)
+man_page_hint = '''
+If you are looking for the man pages of http/https commands, try one of the following:
+    $ man http
+    $ man https
+
+'''
+
+options = parser_to_parser_spec(parser, man_page_hint=man_page_hint, source_file=__file__)
 generate_subparsers(parser, parser, COMMANDS, options)