First implementation of the specification checking

Probably there are bugs around
Renamed method and fixed doc
Added files for checking the spec consistency
Added failing test for the duplicated dropdowns
Fix for duplicated dropdown
Merge pull request #31 from melmothx/topic/duplicated-dropdowns

Fix duplicates in dropdowns.
Bump up version number.
Prepare Changes and README files for upcoming release.
Top level containers should affect lists too.

Due to recursion, containers didn't work as expected inside lists.

This change seems to have duplicated code, but it's a minor one.
Actually, it save some CPU cycles, because containers are scanned only
at top level, instead of at each recursion.

The first block cuts the elts before processing values and lists.

The last block assert that previously cut elements are still cut,
because the value processing paste them back (apparently).
Merge pull request #32 from melmothx/topic/list-global-containers

Top level containers should affect lists too.
Bump up version number.
Prepare Changes and README files for upcoming release.
Merge pull request #30 from melmothx/feature/checking

Check for dangling specification elements.