* add expanded type_size specification
* add some more checks for type_size_max
* continued work on getting type sizes more flexible
* make some more tweaks to option to split up validate and reduce sections
* git rid of exceptions on the type_size functions exceptions, allow any number to be entered for the min and max and don't make a distinction between flags and other types.
* add expected count
* add the allow extra args flag in an option
* start working in allow_extra_args
* write some stuff in the book, and continue working on the failing test cases
* fix a few more of the helpers tests
* a few more test cases running
* all tests pass, fixing calls in ini files
* get vector<pair> working and all tests passing
* change callback to use reference to remove allocation and copy operation
* add support and test for vector<vector<X>>
* change Validators_ to validators_ for consistency
* fix linux warnings and errors by reording some templates and adding some typename keywords
* add support for std::vector<X> as the cross conversion type so optional<std::vector<X>> is supported using the full template of add_option.
* a few more test cases to take care of some coverage gaps
* add missing parenthesis
* add some more tests for coverage gaps
* add test for flag like option
* add transform test for `as<X>` function and make it pass through the defaults
* add a few more tests and have vector default string interpreted correctly.
* add test for defaulted integer, and route default string for defaulted value which would otherwise be empty
* some code cleanup and comments and few more test coverage gap tests
* add more tests and fix a few bugs on the type size and different code paths
* remove path in results by fixing the clear of options so they go back to parsing state.
* get coverage back to 100%
* clang_tidy, and codacy fixes
* reorder the lexical_conversion definitions
* update some formatting
* update whitespace on book chapter
* First streaming version
* Using to_string instead
* Switching to new backend
* Moving to capture function for defaults
* Rename capture_default + _str
* defaultval -> default_str, added always_capture_default
* Fix style
* Adding tests and docs to readme
* Dropping macOS on Travis (supported through Azure)
