[C++ Toolkit ANNOUNCE] MSVC6 C/C++ compiler support dropped; use MSVC 7(.NET) instead

[Denis Vakatov]

1) We have stopped support of MSVC6 compiler for the NCBI C++ Toolkit.

2) The next public release of the C++ Toolkit will be the last one working
   with MSVC6. It's made of the source snapshot made in the beginning of June.

3) The docs on working with MSVC7 are here:
      http://www.ncbi.nlm.nih.gov/books/bv.fcgi?call=bv.View..ShowSection&rid=toolkit.section.ms_vcpp_net