This includes the following improvements:
- The type of the style object is now called 'Style' rather than 'dummy'.
- The new make_style() function allows generating a Style object directly
from a config string. Before the only way to get a style object was
through the environ and it also required that the terminal supported
colors which isn't necessarily the case when testing.
- The output of no_style() is now cached with @lru_cache.
- The output of no_style() now has the same set of attributes as the
other Style objects. Previously it allowed anything to pass through
with __getattr__.
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