Implement getters for data in the fast5 files

[kdoroschak]

Kinds of data to retrieve:

• Raw signals
• Metadata
  • duration
  • start time
  • channel number
• Classification results (assuming classification already happened)
• Reads passing a specific filter (that was already run)

Use cases:

• Retrieve all results/data from a single file, e.g. list of all reads passing the filter in one fast5
• Get info for a certain read_id, given just the read_id and the directory of fast5 files (you shouldn't need to know exactly which file it's in)
• Retrieve all results/data from the entire dataset across all fast5 files
  • Keep ordering in mind, how do we guarantee (or should we guarantee) the same order every time you call this function?