options::option_set implementation.
easy integration with options::option_set.
options::wrapped_option implementation.
BUNSAN_CURL_OPTION_WRAPPED() implementation.
options::wrapper::bool_{,01,02} implementation.
Behavior options declaration.

* verbose
* header
* noprogress
* nosignal
* wildcardmatch
easy: copy implementation.
basic_error bug fix.
detail::easy::setopt() implementation.

options::wrapped_option::init() refactoring.
detail: one_step_iterator and make_one_step_range() implementation.
options::option: id() -> ids().
options::option{,_set}: init() -> setopt().
options::option_set::add() refactoring.
options::option_set::add_and_setopt() implementation.

easy::set_() refactoring.
options::option_set::setopt() bug fix.
options::option_set style fix.
options::wrapped_option style fix.
options: wrapped_option -> wrapper::wrapped_option.
detail::one_step_iterator refactoring.
options::wrapper::wrapped_option refactoring.