Fixed a bug where giving lume.slice() a negative j index (or no j index)
would not result in the correct slice -- the behaviour now correctly
matches that of string.sub() when passing a negative j index.
* The functions which lume.fn() and lume.once() return now return their
inner functions' return value instead of nil
* Moved lume.once() in lume.lua and README.md to be near its similar
functions -- lume.fn() and lume.time()
* The functions lume.any() and lume.all() now have a default function if
one is not provided -- their default behaviour with a single argument
now matches that of Python.
* Updated README.md to reflect changes
* Fixed typo in lume.any()'s example in README.md
* Incremented version revision number
Changed the lume.set(), lume.merge() and lume.filter() functions to take
the argument `retainkeys` instead of `isarray`, and to treat the table
as an array by default (avoiding sparse arrays) instead of treating the
table as an associative array by default (retaining keys).
