add truncate for s3
some fixes for the new write operations
import truncate
add truncate to webdav
doc fixes
Merge pull request #82 from lavelle/write-fixes

Some fixes for the new write operations
more robust truncate test
wrap lines
align closing braces
test truncate for zero case
handle truncate extend case
extract blob conversion function into util method
remove duplication in truncate test
Merge pull request #81 from lavelle/truncate

Add truncate operation