fix API#auth= parameter name
fix API item store

As the symbol key was nil, only one Item was ever created.
tests: move test/unit requirement to helper
always normalize item IDs
Fix ItemCollection#[]

* make sure String keys are used, not symbols
* default to retrieving the whole list, until alternative is implemented
fix ItemCollection#range_offset

Variable name error introduced when refactoring now removed.
fix ItemCollection#range_offset

Take into account that min is in the range.
ItemCollection#request: fix range requests

Also document that ranges are zero-based.
fix ItemCollection: require missing local_filter.rb
add some tests for ALD::API and ALD::API::ItemCollection