Various commands the main SQLite shell has but ours doesn't, or additional flags, and some code cleanups.

• look for sys.version_info in code
• Bare excepts (usually for py2 issues)
• Investigate expert mode- was apswtrace: see .expert mode in sqlite cli #324 - not doing, wraps a virtual table extension
• .open
• automatic formatting for explain/explain query plan
• .connection to list and switch connection
• "Connected to transient memory database" message at startup if no db supplied
• Use asciinema style recording for shell example in doc (not doing)
• .auth (not doing)
• .cd
• .changes
• .close
• .dbconfig
• .dbinfo
• .once / .excel (not doing)
• .explain should be different
• .lint - not doing, just shows some stuff about foreign keys
• .log
• parameter bindings
• .shell / .system - synonyms, only shell added
• .stats (not doing)
• .timeout
• .version
• .vfsinfo / .vfslist / .vfsname
• pipe in .import - was Support pipe in .import filename #141 - not going to do because would have to spool to a tempfile so user may as well do it
• .exit can take code to exit with
• .quit is not a synonym for .exit - removed since it has no useful purpose
• _terminal_width can use os method instead
• manual caching of stuff like completions should use properties
• The shell doc built by sphinx should use the long help information, heading per command, index entry etc
• Update pragmas - eg function_list is missing
• Long rant about uniicode in shell.rst should be shortened
• shell.rst "Example" should become "Programmatic usage"