Ensure all docs are correct for v2 release

[kbknapp]

• src/app/macros.rs
• src/app/meta.rs
• src/app/mod.rs
• src/app/parser.rs
• src/app/settings.rs
• src/args/arg_builder/mod.rs
• src/args/arg_builder/flag.rs
• src/args/arg_builder/option.rs
• src/args/arg_builder/positional.rs
• src/args/matched_arg.rs
• src/args/subcommand.rs
• src/args/group.rs
• src/args/arg_matcher.rs
• src/args/mod.rs
• src/args/any_arg.rs
• src/args/arg.rs
• src/args/arg_matches.rs
• src/args/settings.rs
• src/fmt.rs
• src/suggestions.rs
• src/utf8.rs
• src/errors.rs
• src/lib.rs
• src/osstringext.rs
• src/usage_parser.rs
• src/macros.rs
• examples/01a_quick_example.rs
• examples/01b_quick_example.rs
• examples/04_using_matches.rs
• examples/05_flag_args.rs
• examples/06_positional_args.rs
• examples/08_subcommands.rs
• examples/09_auto_version.rs
• examples/10_default_values.rs
• examples/11_only_specific_values.rs
• examples/15_custom_validator.rs
• examples/16_app_settings.rs
• examples/17_yaml.rs
• examples/17_yaml.yml
• examples/01c_quick_example.rs
• examples/02_apps.rs
• examples/03_args.rs
• examples/07_option_args.rs
• examples/12_typed_values.rs
• examples/13a_enum_values_automatic.rs
• examples/13b_enum_values_manual.rs
• examples/14_groups.rs
• examples/18_builder_macro.rs
• tests/app.yml
• tests/multiple_occurrences.rs
• tests/yaml.rs
• tests/app_settings.rs
• tests/conflicts.rs
• tests/help.rs
• tests/hidden_args.rs
• tests/possible_values.rs
• tests/subcommands.rs
• tests/unique_args.rs
• tests/utf8.rs
• tests/version.rs
• tests/flags.rs
• tests/groups.rs
• tests/opts.rs
• tests/positionals.rs
• tests/require.rs
• tests/tests.rs
• tests/multiple_values.rs
• tests/posix_compatible.rs

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• Ensure all examples work and pass
• Ensure all examples have ending markdown

[kbknapp]

Closed with #395