v0.3.0-rc.1

• fixed enum member name to be on par with the others
• tested a bit and changed methods to work with provided buffers (5.7)
• added next() as a method to return reference to new SubmissionEntry
• changed prep methods to allow new chain syntax:

io.next
    .prepRecv(ctx.fd, grid, len)
    .setUserDataRaw(someData)
    .flags |= SubmissionEntryFlags.BUFFER_SELECT;