add isolated attribute to adapters
Merge pull request #54 from slang800/isolated

add isolated attribute to adapters
move requireEngine into Adapter as a private func

also remove error rethrow
add yade to adapter/engine map
rename customPath to enginePath and document it
switch from @engine.__accord_path to @enginePath

also refactor clientHelpers to return a promise. this will require a
version bump
update tests
fix examples in readme

remove bad error handling and don't call toString on functions or
strings
remove util.format - mocha now does this