(urgent) Use Glossarist gem instead of manual splitting (`split_codes.rb`) to generate Metanorma AsciiDoc

We are using complex input from IEV but the split_codes.rb script is very rudimentary.

e.g.
```yaml
eng:
id: 192-01-03
terms:
- type: expression
normative_status: preferred
usage_info: in dependability
designation: system
definition: set of interrelated items that collectively fulfil a requirement
language_code: eng
notes:
- A system is considered to have a defined real or abstract boundary.
- External resources (from outside the system boundary) may be required for the
system to operate.
- A system structure may be hierarchical, e.g. system, subsystem, component, etc.
- Conditions of use and maintenance should be expressed or implied within the requirement.
examples: []
entry_status: valid
authoritative_source:
- ref: IEC 60050-151:2001
clause: 151-11-27
link: https://webstore.iec.ch/publication/176
relationship:
type: modified
modification: by extension to suit the dependability context
original: IEC 60050-151:2001, 151-11-27, modified by extension to suit the dependability
context
date_accepted: '2015-02-01T00:00:00+00:00'
date_amended: '2015-02-01T00:00:00+00:00'
review_date: '2015-02-01T00:00:00+00:00'
review_decision_date: '2015-02-01T00:00:00+00:00'
review_decision_event: published
```

Metanorma has been updated to use the Glossarist gem so we just need to add a `GlossaristConcept.new.to_mnadoc` method.

See: https://www.metanorma.org/author/topics/document-format/section-terms/