Use ".ihm" file suffix instead of ".cif". about ihmcif

[jdwestbrook]

While separation of content and format are important considerations adopting naming
conventions, overloading the file name extension to carry both of these details is not path that we would prefer to follow. We would prefer to follow to follow a convention where the file extension
identifies the parsing syntax, and then separately specify the content specification (e.g. supporting dictionary/schema). For example, in file released by PDB in recent years, audit records are provided in the mmCIF files and schema records in PDBML files to identify content specifications.

As a practical alternative to using the file extension to convey content details, we would prefer to
use a combination internal audit records and standard file naming templates to convey this
information. For example, accession-code-ihm.cif ) .

[benmwebb]

Related discussion in Chimera issue 16277.

[benmwebb]

One proposal from last week's Skype meeting was to use the extension .ihm.cif for these files. This allows for packages such as ChimeraX to recognize the files as using the IHM dictionary based purely on the file extension, while at the same time allowing non-IHM software (such as legacy Chimera) to visualize at least the atomic information in the file.