Make _storage_format_specification a method.

[josiah-wolf-oberholtzer]

There are currently two format-related properties on AbjadObject subclasses:

• _storage_format_specification
• _repr_specification

When hasattr(..., '_storage_format_specification') is called on an AbjadObject subclass instance, the property is evaluated. Then, typically, the property is accessed. This effectively totals a double evaluation of configuring and instantiating a StorageFormatSpecification object.

We should convert all such properties to _get_...() methods to avoid these double evaluations triggered by hasattr().

[trevorbaca]

In June 2017 _get_storage_format_specification() now exists.

There are what look to be ancient (and probably unused) references to _repr_specification in StorageFormatAgent:

tools/systemtools/StorageFormatAgent.py
85:            hasattr(self._client, '_repr_specification') or
306:            spec = getattr(self._client, '_repr_specification', None)
309:                via = '_repr_specification'
596:            '_repr_specification' in dir(self._client) or
597:            hasattr(self._client, '_repr_specification') or
609:            specification = getattr(self.client, '_repr_specification',
621:            specification = getattr(self.client, '_repr_specification',

Will leave issue open until _repr_specification references are removed from StorageFormatAgent.

[trevorbaca]

Done in 2.21.