Move error pushing to src/util.c
README: Whitespace
src/journal.c: Start work on journal reading; bound `sd_journal_open*`
src/journal.c: Add :next(_skip), :previous(_skip) methods
Move defines to headers
src/journal.c: Add sd_journal_seek* bindings
src/journal.c: bind sd_journal_{get,enumerate,restart}_data()
src/journal: Expose journal methods table
src/journal.c: Expose sd_journal_{s,g}et_data_threshold()
src/journal.lua: Add lua iterator for enumerating fields
src/journal: Add :get() method