[#DCE9E0DE35F592C70096C7DC5A6E4B5D6E858A57]
Replace elements
iterator replace( iterator pos, param_view const& p);
This function replaces the contents of the element at `pos` with the specified param.
All iterators that are equal to `pos` or come after are invalidated.
url u( "?first=John&last=Doe" );
u.params().replace( u.params().begin(), { "title", "Mr" });
assert( u.encoded_query() == "title=Mr&last=Doe" );
Linear in `this->url().encoded_query().size()`.
Strong guarantee. Calls to allocate may throw.