Fix snips-nlu-metrics import

[adrienball]

Added

• Add a --config argument in the metrics CLI

Changed

• Replace "parser_threshold" by "matching_strictness" in dataset format
• Optimize loading and inference runtime
• Disable stemming for intent classification in default configs

[codecov-io]

Codecov Report

Merging #700 into master will decrease coverage by 0.02%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master     #700      +/-   ##
==========================================
- Coverage   87.92%   87.89%   -0.03%     
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  Files          64       64              
  Lines        3684     3684              
  Branches      672      672              
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- Hits         3239     3238       -1     
- Misses        344      345       +1     
  Partials      101      101