Slyp

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- Unexpected errors encountered when parsing files are now reported as failures, rather
than causing ``slyp`` to abort
- Replace E110 with autofixer behavior, which rewrites the return of a known-``None``
variable immediately after testing it to return ``None`` instead
- Replace W102 with autofixer behavior, which parenthesizes multiline
concatenated strings in dict elements
- Replace W103 with autofixer behavior, which parenthesizes multiline
concatenated strings in tuple, list, and set literals if there is more than
one element
- Add the ``--only`` flag, enabling ``--only=lint`` or ``--only=fix`` to run only
the linting or fixing
- Add basic support for reading data from stdin, in which case
- ``--only`` must be used
- if ``--only=fix``, then the resulting file is always written to stdout
- Implement an additional check for unnecessary string concatenation, E101

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- Replace the W101 lint with autofixer behavior, which will insert the
necessary parentheses
- Improve the way that files are handled to read only once from disk per file
- ``slyp`` now processes files in parallel and produces its output at the end of
its run (with some simple sorting)

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- Fix passing file caching to correctly record successes after a failure
- The cache implementation has been improved to cache by file contents rather
than path, allowing duplicate files to share a cache entry

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- Various performance improvements, especially for fixing
- ``slyp`` will now cache results for files which pass all checks in
``.slyp_cache``, thus avoiding rechecking files which pass and have
not changed

- this behavior can be disabled with ``--no-cache``
- the cache is maintained independently for each possible set of
``--enable/--disable`` options passed to ``slyp``
- projects which fully pass ``slyp`` checking should experience the greatest
improvement -- as great as 50x faster on sizable production codebases with
a populated cache

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- Fix the handling of parenthesized lambdas in the fixer. The innermost
parentheses arounda lambda are now preserved.
- Minor speed enhancements.
- Fix the handling of autofixing in certain expressions when there is no
whitespace between a hard keyword and a parenthesis, inserting spaces when
necessary.
- Fix unnecessarily parenthesized ``with`` and ``from ... import ...`` statements.
- Preserve parentheses immediately under unary operations, as they may aid
readability.
- Remove W120. It is automatically fixed by the latest ``black`` versions.
- In restricted cases, the fixer will now automatically join implicitly
concatenated strings when there is no newline. This autofix covers some cases
of E100.

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- Preserve the innermost parentheses when used inside of splat-argument
expansion. e.g., ``foo(*("a b".split()))`` is NOT fixed to
``foo(*"a b".split())``. This is semantically equivalent to the version with
the parentheses removed, but not as obvious to readers.