Trying to localize the reason of the test failure on Sandia-Darwin.
Simplified matching function backend selection. Added backend for std::regex.
Updated docs.
Made std_regex.hpp not hard fail the self_container_header test in case if STL does not support std::regex.
Added configuration macros for regex backend selection. The backend is used by string matching filters parsed from strings and settings.
Removed checkpoints. The crash on Sandia-Darwin happens when the formatter is invoked. Further investigation needed.
Added missing #include <ios>.
Interfacing with various regex backends made more accurate.
Switched to Boost.Regex regex backend by default. Performance tests showed that it is faster than Boost.Xpressive for small string matching. std::regex is the slowest across all tested platforms (MSVC 12, gcc 4.8, clang 3.4). Boost.Regex also produces smaller executables than Boost.Xpressive.
Do not depend on Boost.Regex if settings parsers or default factories are disabled.