Inconsistent naming in the Builder APIs

[asomers]

capsicum contains three Builder structures

• RightsBuilder => FileRights
• IoctlsBuilder => IoctlRights`
• FcntlsBuilder => FcntlRights

There are two inconsistencies here:

• The usual pattern used by other crates is XBuilder => X. But we leave Rights out of the builder's name.
• The pluralization is weird. It's "Ioctls" in the builder, but "Ioctl" in the build structure. This wouldn't be a problem if it weren't for the first thing.

I suggest one of two solutions:

• Put "Rights" in the builder name, like IoctlRightsBuilder
• Use modules to provide namespacing. e.g. capsicum::ioctl::RightsBuilder => capsicum::ioctl::Rights.