Get rid of .metadata files

[davidemoro]

.metadata files was introduced (but never released) in #5.
Since the scenarios are defined with YAML format, we are going to use a single file containing everything you need for defining and decorate your scenarios.

You might have an optional YAML document on top of your scenario containing metadata.

[codecov-io]

Codecov Report

Merging #65 into features will increase coverage by 0.84%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##           features      #65      +/-   ##
============================================
+ Coverage     92.41%   93.26%   +0.84%     
============================================
  Files             6        6              
  Lines           290      282       -8     
============================================
- Hits            268      263       -5     
+ Misses           22       19       -3

Impacted Files	Coverage Δ
pytest_play/engine.py	100% <100%> (ø)	⬆️
pytest_play/plugin.py	81.18% <100%> (+1.37%)	⬆️

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