[WIP] Add utils subcommand

[luizirber]

Exploring a possible fix to #201

• Is it mergeable?
• make test Did it pass the tests?
• make coverage Is the new code covered?
• Did it change the command-line interface? Only additions are allowed
  without a major version increment. Changing file formats also requires a
  major version number increment.
• Was a spellchecker run on the source code and documentation after
  changes were made?

[codecov-io]

Codecov Report

Merging #236 into master will decrease coverage by 4.7%.
The diff coverage is 75%.

@@            Coverage Diff             @@
##           master     #236      +/-   ##
==========================================
- Coverage   90.75%   86.05%   -4.71%     
==========================================
  Files          33       13      -20     
  Lines        5010     1958    -3052     
  Branches       36       52      +16     
==========================================
- Hits         4547     1685    -2862     
+ Misses        463      263     -200     
- Partials        0       10      +10

Impacted Files	Coverage Δ
sourmash_lib/__main__.py	91.66% <75%> (ø)
sourmash_lib/__init__.py	100% <0%> (ø)	⬆️
tests/test_lca.py
sourmash/lca/lca_utils.py
sourmash/lca/command_rankinfo.py
benchmarks/benchmarks.py
tests/test_api.py
sourmash/lca/command_summarize.py
sourmash/logging.py
sourmash/commands.py
... and 35 more

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