set up basic API for Ramsey::Index, remove old code from ramsey/index.rb
configure path, not name, in config block.
rough in the index
spec Ramsey::Index#delete!
spec Ramsey::Index#update!
rough in Ramsey::Index#load! specs
Implement #load! on Index
implement #save! on index

needs integration specs
factor fixture stuff into a shared_context
implement uses_fixtures to use /tmp and just provide paths
add integration spec covering dumping an index to file and reloading it.
extend the save and load spec to cover multi-property indices.