logger.go: Condense log level labels

Condense names to four characters so that the remaining output lines up with
the previous and post output lines.
logger.go: Add Ltree and LshowIndent

Add flags for controlling indentation based on the stack position from where
the log output call was made.
logger.go: Add LdebugFlags
logger.go: Documentation fixes
Fix expect length for TestMultiStreams()
Add TestTreeDebugln()

Refactor from TestHeirarchicalPrintln()
template.go: Remove space after .Indent