This was causing a return value != 0 even when all interfields were
valid.

Revision date was (most likely) a legacy name that never had its
`lvcnrpy` integration test updated.

One addition convinience method to facilitate the modification of
datasets fields.

The two additional convinience methods facilitate the modification of
fields other than the (now) optional field derived field test classes
represent.

Add optional attribute to specification fields

See merge request !7

- `auxiliary-info` is specified as an optional field.

- `lvcnrcheck` gives a return code of `0` if the only failing fields are
  option and missing.

  However if fields are present and fail for other reasons (for example
  wrong type such as `str` when it should be `int`) then the return code
  will be `1`.

Use format field in file as lvcnrcheck default

See merge request !6

Falling back to format level 1 if the field is missing in the file to be
checked.

Update lvcnrcheck with pass/fail information

See merge request !5

- Fixes #2
- See merge request !3

`galadirith/lvcnrpy:v1.0.0` already has all test dependencies to
dramatically reduce test suite run time on Gitlab CI.

The `Spec` class family were originally set up to work using class
methods. This was natural because each `Spec` derivative only
represented a single field.

With the addition of the `Amplm` and `Phaselm` specs, this was no longer
true, with each of these specs required to represent a collection of
fields. While initially attempted to use instances for these `Specs` and
classes+classmethods for the remaining specs, to much off the logic
required casing on the `Spec` being an instance of class, it was decided
to only use classes and classmethods.

In the end this resulting in a massive anti-pattern, defining a class
factory in place of instance initialisers in the `Amplm` and `Phaselm`
classes, and a general bad logic. It made sense to use classmethods
before, but in no longer did.

This commit refactors most classmethods as instance methods (with a
couple left as classmethods because theydo not reference the parent
object, and could infact be staic methods). While a couple of
expressions required additional `()` to instance `Specs`, overall the
logic has been greatly simplified and actually demonstrated that the
classmethod paradigm previously used had significantly little benifit.

Add error to handle case when absolute value of the mode's order
exceeds its degree.

- Specs have been added that represent phase and amplitude modes.
- 5 degrees with everyone order of phase and amp modes fields are now
  created by `createValidSim`
- `lvcnrcheck` looks for and validates phase and amp modes.

- Fix romspline validation #1
- See merge request !2

The test classes test the Specs and `lvcnrcheck`, that they only check
for invalid fields right now doesn't matter and identifying invalid
tests is for the test class methods name to confer.

To distinguish the human readable `name` from the `name` of
`InvalidValue`.

Renamed and redoc'd to more accuratley describe its function.

Identifiers were modified from ~component to ~subfield to make
identifiers consitent.

Each `Spec` derived class is now responsible for creating a valid field
that it represents in a supplied `Sim` instance.

Towards this, logic for creating valid fields was removed from the test
helper.

See merge request !1

`Specs.valid` now return `Error` objects and the logic of generating
errors and associated messages have been refactor to their own dedicated
module.

Much error message logic has now been removed from `lvcnrcheck` with
only specific cases handled as nessesary, right now only a `Missing`
`Error` needs to be cased.

Refactor generation of flattened attributes for simulations.