Fix TPI NVM Write handler -- AVRStudio sends out writes in page sized chunks, not byte sized chunks.

Add first draft of the TPI NVM commands for reading, writing and erasing a target. Needs testing when physical access to a part is available.

Add dummy undocumented TPI XPROG parameters to the AVRISP project so that TPI programming mode can be entered.

Fix mistakes in the XPROGTarget.c/.h files for TPI mode software USART clock rate and PDI mode XPLAIN board autoconfiguration.