Add support for parallel jobs for NearestNeighbors search with n_jobs parameter

[paullo0106]

Proposed changes

This fixes #386 by adding support for parallel jobs for NearestNeighbors search with n_jobs parameters, -1 is the default value which uses all processors

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• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
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[ppstacy]

LGTM, thanks!