Use the libsodium-0.1 release

This should be quicker (no need to run autotools) and also more stable (no changes to libsodium breaking the build).
Still build based on libsodium dir

Less things to change when we increment the number this way!
Merge pull request #7 from namelessjon/libsodium-0.1

Use the libsodium-0.1 release