#include cleanup (#231)

* update library headers to have self-contained #includes

* update gha ci to run for feature/** branches

include/boost/regex/v5/mem_block_cache.hpp

@@ -18,6 +18,8 @@
 #ifndef BOOST_REGEX_V5_MEM_BLOCK_CACHE_HPP
 #define BOOST_REGEX_V5_MEM_BLOCK_CACHE_HPP
 
+#include <boost/regex/config.hpp>
+
 #include <new>
 #ifdef BOOST_HAS_THREADS
 #include <mutex>
@@ -31,6 +33,7 @@
   #endif
 #endif
 
+
 namespace boost{
 namespace BOOST_REGEX_DETAIL_NS{