rust: Add bindings for nbdkit_parse_size and nbdkit_parse_bool
Extend the ramdisk example with an optional size= parameter, eg:
$ nbdkit -fv ./plugins/rust/target/release/examples/libramdisk.so size=1G
--run 'nbdinfo "$uri"'
Extend the ramdisk example with an optional size= parameter, eg:
$ nbdkit -fv ./plugins/rust/target/release/examples/libramdisk.so size=1G
--run 'nbdinfo "$uri"'