llkd: llkSplit should prevent empty entries

Add "false" as an option fed into llkSplit to be equivalent to empty,
as a truly empty list is replaced with the internal defaults.  Ensure
that no empty entries are added to the returned list.  Add some
additional provisos to README.md, as well as the explanation of what
"false" means for the associated properties.

Test: llkd_unit_test
Bug: 33808187
Bug: 111910505
Bug: 80502612
Change-Id: Iac0457ea1f6cd559b0875f9871dbae839001276d