Added timer library, amended other libraries

Added timeit library:
timeit.new() - creates a new timer object
timeit.start() - starts the timer
timeit.stop() - stops the timer and returns the time difference
timeit.next() - restarts the timer and returns the time difference until
that point
timeit.check() - returns the time difference without stopping the timer

Added to logger:
flog(...) - logs to file 'lua.log' in the same directory as the addon
with full timestamp
table.tovstring(t) - left out initial indent on open brace

Added to tablehelper:
Changed the initial description
table.arrmap(t, fn) - fixed the iteration over nil values