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[skip ci]
Displays a warning for READ_THEN_WRITTEN files

They are a reproducibility issue.
Adds docstrings to all modules
Merges canonicalize.py into pack.py

It made sense for this to be under the tracer package, but it's just too
small.
Adds LICENSE.txt to packages

[skip ci]
Fixes typo

[skip ci]
Fixes major typo in tracer
Factors get_files()
Only displays read_then_written warning once

Prints out warning once with the list of files instead of printing it
again for each file.
Identifies input files
Adds 'input_files' to 'runs' in configuration
Labels input files
Uses resolved filenames for input files
MANIFEST.in: include header files in sdist
Adds 'reprounzip info' command
Makes entry points return some information

The setup function defined by the entry_point mechanism now returns a
list of dicts, which each contain information about a specific unpacker.
The "official" entry_point have been updated to return that information,
which currently includes:
  - 'name', the readable name of the unpacker (that is the argparse
    command group)
  - 'test_compatibility', which indicates if the unpacker will work on
    the current machine with the given pack file

This will be useful to list and test the available unpackers.
Merge branch 'unpacker-info' into 'info-command'

Conflicts:
	reprounzip/reprounzip/reprounzip.py
Makes 'reprounzip info' print compatible unpackers
Simplifies test_compatibility
Simplify test_compatibility protocol