add missing Logger methods

Conflicts:
	src/Core/Logger.type.plb
	src/Core/Logger.type.pls
add NULL check and version check
fix query in get_log_level

Conflicts:
	src/Util/get_log_level.fnc.plb
Merge branch 'master' of https://github.com/Shoelace/log4oracle into development

Conflicts:
	src/Core/LogImpl.pkb
	src/Core/ThreadContext.pkb
	src/Util/get_log_level.fnc.plb