Corrected compiler switches to enable AVX2 and SSSE3 for Intel Compiler. Disabled some bogus warnings as well.
Removed most of Boost.Spirit from the parameter partsers to speedup compilation and reduce binary sizes. This also significantly reduces memory consumption in case of Intel Compiler (down by ~600MiB).
Added a missing include.
Added -lsocket for QNX.
Added more linking switches for compatibility with different platforms.

The switches were taken from Boost.ASIO Jamfiles as most of them are needed to build network-related code. Also replaced the linkflags with libraries so that Boost.Build takes care of the actual flags.
Use low-level Qi extractors instead of qi::parse to reduce compile times and binary sizes.
Extracted text_multifile_backend implementation to a separate file.
Disabled 'may be used uninitialized' warnings for gcc caused by boost::optional.
Disabled more of Intel warnings.