Api/remove ml

[ClaudiaComito]

Description

Removing the ml sub-module, cluster and regression are now directly below the ht module namespace. Also, provided __init__.py file to lasso/tests which had gone untested and unnoticed so far.

Fixes: #398

Changes proposed:

Type of change

Select relevant options.

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

Are all split configurations tested and accounted for?
[x] yes [ ] no
Does this change require a documentation update outside of the changes proposed?
[x] yes [ ] no
Does this change modify the behaviour of other functions?
[ ] yes [x] no
Are there code practices which require justification?
[ ] yes [x] no

[codecov]

Codecov Report

Merging #431 into master will decrease coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #431      +/-   ##
==========================================
- Coverage   96.57%   96.57%   -0.01%     
==========================================
  Files          55       54       -1     
  Lines       11951    11950       -1     
==========================================
- Hits        11542    11541       -1     
  Misses        409      409

Impacted Files	Coverage Δ
heat/core/regression/lasso/lasso.py	90.19% <ø> (ø)
heat/core/cluster/kmeans.py	81.15% <ø> (ø)
heat/core/regression/__init__.py	100% <ø> (ø)
heat/core/cluster/__init__.py	100% <ø> (ø)
heat/core/regression/lasso/__init__.py	100% <ø> (ø)
heat/core/cluster/tests/test_kmeans.py	80% <100%> (ø)
heat/core/regression/lasso/tests/test_lasso.py	94.11% <100%> (ø)
heat/__init__.py	100% <100%> (ø)	⬆️

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