Version 1.6.2: Help-all

This version fixes some formatting bugs with help-all. It also adds fixes for several warnings, including an experimental optional error on Clang 7. Several smaller fixes.

* Fixed help-all formatting [#163]
    * Printing help-all on nested command now fixed (App)
    * Missing space after help-all restored (Default formatter)
    * More detail printed on help all (Default formatter)
    * Help-all subcommands get indented with inner blank lines removed (Default formatter)
    * `detail::find_and_replace` added to utilities
* Fixed CMake install as subproject with `CLI11_INSTALL` flag. [#156]
* Fixed warning about local variable hiding class member with MSVC [#157]
* Fixed compile error with default settings on Clang 7 and libc++ [#158]
* Fixed special case of `--help` on subcommands (general fix planned for 1.7) [#168]
* Removing an option with links  [#179]

[#156]: https://github.com/CLIUtils/CLI11/issues/156
[#157]: https://github.com/CLIUtils/CLI11/issues/157
[#158]: https://github.com/CLIUtils/CLI11/issues/158
[#163]: https://github.com/CLIUtils/CLI11/pull/163
[#168]: https://github.com/CLIUtils/CLI11/issues/168
[#179]: https://github.com/CLIUtils/CLI11/pull/179
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