Peter M. Groen / CLI11

* add some tests with default capture on the two parameter template and some notes about it in the README.md

remove the test from visual studio 2015
vs2015 doesn't seem to properly deal with is_assignable in the cases we care about so make a standalone version that is more direct in what we are doing

add version to appveyor and add some notes to the readme

fix a few test cases to make sure code is covered and test a few other paths

remove unneeded enum streaming operator

add some diagnostic escapes around trait code to eliminate gcc Wnarrowing warnings

work specification of the template operations

remove optional add some templates for options conversions

add the two parameter template for add_option

* Fix some comments from Code review and add more description

* fix case when string_view doesn't work to append to a string.

* This PR also addressed #300

* modify lexical_cast to take  const std::string &, instead of by value to allow string_view in a few cases

* move delimiter controls to Option vs in the App callbacks

Add a test that creates and uses a custom parser to store a value

add a check around regex to see if it is working

fix warning in AppTest from gcc

Now use type_name and type_size instead of set_custom_option.

* set_default_str and set_default_val update

* Fixes for style checking