Today's changes

• Avoid memcpy when possible during buffered read (send directly from buffer memory)
• SOCK_RXRING option is off by default. It appeared that stupid but aligned buffer often faster. (To be investigated)
• All IO buffers now aligned to page boundary instead of 512 bytes. It also sometimes faster
• Fixed long delay on exit when compiled without SOCK_RXRING
• More flexible selecting blocks/frames count for mapped buffer if SOCK_RXRING enabled
• Added optional CRC8x4 data verification support. Normally its not necessary cause ethernet hardware already uses CRC32 for packets data integrity verification and this option defeats performance. However it can be useful to diagnose hardware problems or if user is paranoiac enough. To enable its support by this target uncomment '#define SUPPORT_CRC' in tuneup.h before making project. Note that initiator should be able to deal with this option and should request it explicitly as extension otherwise it will have no effect.