Use of unstable features

[Fraser999]

The following feature gates are being used (which disallow this to be built on the Beta or Stable Rust channels):

#![feature(convert, core)]
#![feature(convert)]

[benjaminbollen]

we use convert in src/error.rs, but that usage is stable now
we don't use core, so that is easily removed,
the remaining unstable use of convert is in NameType::get_full_id() but we never use that; so I can simply remove remove get_full_id, or we can find a better way to append strings

[benjaminbollen]

the story is a bit more involved. I was too quick to think that #[feature(core)] could be dropped from the example (refer to failed #561).

Also removing "get_full_id" from NameType is trivial, as it is unused; but the unit tests for debug_output of the NameType does use the get_full_id to check the correctness of the debug output.

This needs a better was of unit testing the NameType debug output. Can not be a blocker, but might be a bit more hairy.

[benjaminbollen]

almost resolved by latest work in example. Only the nametype tests use an unstable feature for a secondary way of testing the debug representation of NameType; the test need to be rewritten without the unstable feature