Allow different ir_metadata format variants

[janheinrichmerker]

The ir_metadata should be able to be exported to files with the following conventions based on the file extension:

• *.ir_metadata/*.ir-metadata:
  uncompressed file with ir_metadata.start prefix and ir_metadata.end suffix
• *.ir_metadata.yml/*.ir-metadata.yml/*.ir_metadata.yaml/*.ir-metadata.yaml:
  uncompressed YAML file (i.e., without prefix/suffix)
• *.ir_metadata.gz/*.ir-metadata.gz:
  Gzip-compressed file with ir_metadata.start prefix and ir_metadata.end suffix
• *.ir_metadata.yml.gz/*.ir-metadata.yml.gz/*.ir_metadata.yaml.gz/*.ir-metadata.yaml.gz:
  Gzip-compressed YAML file (i.e., without prefix/suffix)

Supporting these extensions fully supports the usual implementations of the ir_metadata specification.

The change should be implemented in:

• C
• Python (Auto-guess export format and improve ir_metadata handling #43)
• Java (Auto-guess export format and improve ir_metadata handling #43)