Fix string_view::cend() recursively calling self (#27)

`string_view::cend()` was defined as calling `cend()` unqualified, 
resulting in an infinite recursive loop (and inevitable crashes as a
result). The fix here is simple: just define the logic inline, and don't
call `cend()`.

Runners on CI are failing due to being very old/deprecated.

Fixes: #26

Author: ckormanyos

include/bpstd/string_view.hpp

@@ -1186,7 +1186,7 @@ typename bpstd::basic_string_view<CharT,Traits>::const_iterator
   bpstd::basic_string_view<CharT,Traits>::cend()
   const noexcept
 {
-  return cend();
+  return m_str + m_size;
 }
 
 template <typename CharT, typename Traits>