Create an empty metatable for user modules

If a user module is loaded into a global variable the preservation
will restore it to an empty table, wiping out the real module.
Add access to internal data

- initial configuration settings
- column header information
remove unused variable 'seconds_in_minute'
Update the documentation
Issue #17 further parse the syslogtag variable
Fix the circular buffer 'get' beyond the end of the buffer

It now returns nil as specified instead of wrapping around to the
beginning of the buffer.
Fix the %c grammar to use a space padded month
One more tweak to programname

Don't follow the RFC standard just accept what rsyslog outputs.
Merge branch 'dev' into haproxy-grammar

Conflicts:
	modules/date_time.lua
	src/test/lua/circular_buffer.lua
	src/test/test_lua_sandbox.c