When set to true, this config option chooses copying over converting when the
source file is in a lossy format. At the moment, everything except ape, flac,
alac and wav is considered lossy.
This option allows the user to specify the format on the command line
instead of editing the configuration.
The commit also includes some refactoring. In particular adding
arguments to functions to avoid dependence on global state.
Doc and Changelog in next commit
Doing test-specific cleanup in tearDown before general sandbox deletion helps
avoiding contamination of global state between tests when cleanup fails.
Current Windows status:
Ran 1106 tests in 72.373s
FAILED (SKIP=10, errors=13, failures=15)
Closer!
* `encode()` raises an error when the command returns with non-zero exit
status. We catch that in the higher-level conversion functions and skip to
the next item without writing tags.
* Simplified the handling of the `keep_new` flag.
