Add the SQLITE_CONFIG_PCACHE_HDRSZ option for sqlite3_config().
Improved documentation and addition of source-code evidence marks for the
sqlite3_config() interface.
Change the definition of SQLITE_CONFIG_SCRATCH so that at most one scratch
buffer is used per thread.  Use the generic heap memory allocator for the
WalIterator object when running a checkpoint.
Add various requirements evidence marks for sqlite3_config() options.
Improved output formatting for the showstat4 tool.
Add the ".scanstats on" command to the shell tool. Executing this command causes the shell tool to print values from sqlite3_stmt_scanstatus() after each query is run.