Add spec for Roo::Excel#sheets in hopes of reproing #54
Add regression spec for #37

Apparently #parse is pretty weird in that it includes the header
row in the result, as a hash with header keys and values.
Add changelog entries for #37 and #40
Refactor Roo::Google to avoid querying session#spreadsheet_by_key#worksheets twice in #initialize
Move google_drive to a development dependency so that those not using it aren't forced to install it.
Drop unused Google*Error exceptions.
Convert a basic and essentially pointless test to rspec, as it easily bootstraps our specs.

It also exposes that we need a better way of
testing Roo::Google - the test_roo tests seem to
rely on Hugh Mcgowan's google drive account.
Refactor Roo::GenericSpreadsheet#reload to rely on method calls rather than class detection.

And fix that it was broken since our conversion to hash-based options.
Fix that Libreoffice wasn't declared for autoload.
Rename Openoffice -> OpenOffice, Libreoffice -> LibreOffice, Csv -> CSV,
and redirect the old names to the new constants
Rename Roo::GenericSpreadsheet to Roo::Base.
Enable Roo::Excel, Excel2003XML, Excelx, OpenOffice to accept an options hash, and deprecate the old method argument-based approach to supplying them options