Addresses #29: Support missing version-hint.txt and provide additional options

[teaguesterling]

This intends to address #29 by providing some additional options when finding metadata files to use.

This PR essentially adds two parameters to the iceberg functions:

• version - Either a version number of the table to use, or a "hint" filename that should be read to get the latest version.
  Default value: 'version-hint.text' (preserves the previous behavior of looking for a version-hint.text file
  Examples: version='12': Explicitly load table version 12. version='my-custom-version-file.txt': Use version from my-custom-file.txt instead of version-hint.text
• version_name_format - comma-delimited list of format strings that should be tried to find the metadata file name based on the supplied or hinted version.
  Default value: 'v%s%s.metadata.json,%s%s.metadata.json (extends the previous behavior by also checking for a version file without the prefixed "v" in the event the default behavior failed).
  Examples: 'version-%smetadata.json%s' would look for version-42.metadata.json.gz when specified with (..., version='42', medata_compression_codec='gzip')

As was suggested by @lamb-russell, this PR will (eventually) do the following:

• Replace the hard coded "v" prefix being added to the version in "version-hint.txt" with a more flexible printf-style template string that can be specified as a parameter.
• Rework in the metadata functions to explicitly pass the right metadata file version around instead of loading it deep in the stack.
• Capture the appropriate version id earlier from "version-hint.txt"
• Allow a specific version id to be passed in to the iceberg functions (disabling the use of "version-hint.txt")
• Allow a specific version formatter to be passed into iceberg functions
• Update test cases
• Update documentation
• Possibly provide some additional helper functions to find list available versions to make using the id and formatter parameters easier.

[samansmink]

Looks great!