Exporting link url when converting spreadsheet to csv

If the celltype was a link, the behaviour was raising an unhandled
celltype exception. I believe the best solution for this case (at least
for my use case) is exporting the url of the link.
Properly process paths/files with spaces in them.
RSpec >= 2.14 is required for tests to pass
remove duplication in Roo::Base#initialize
prevent ArgumentError: wrong number of arguments (0 for 1) in Roo::Base#find by row number if header_line is not nil
Merge pull request #100 from funkydrummer/funkydroommer

prevent ArgumentError: wrong number of arguments (0 for 1) in Roo::Base#...
Merge pull request #99 from funkydrummer/duplication

remove duplication in Roo::Base#initialize
Merge pull request #98 from monterail/rspec

RSpec >= 2.14 is required for tests to pass
Merge pull request #94 from mbklein/master

Properly process paths/files with spaces in them.
Merge pull request #93 from pedroaxl/master

Exporting link url when converting spreadsheet to csv