Fixed missing LOWER function in map_formulae_to_ruby
Fixed missing LOWER function in map_formulae_to_ruby
Now checks whether sheet names and named references provided by the user actually exist, and if not, aborts
Prepare to release 0.2.4
named_references_to_keep and named_references_that_can_be_set_at_runtime can now be passed a block which will be called with each named reference. Returning true will make the named reference kept / settable
Prepare to release 0.2.5