Add `_estimator_type` in python package

[oooo26]

• add _estimator_type for linear, logistic, poisson, gamma, multitask, multinomial
• support pandas dataframe for fit()
• support non-number classes for classifier (logi & multinomial)
• move ext_module pybind_cabess inside abess package

[oooo26]

Also fix issue #407 .

[codecov[bot]]

Codecov Report

Merging #408 (52a2b1a) into master (3335d9d) will increase coverage by 0.00%. The diff coverage is 97.82%.

@@           Coverage Diff           @@
##           master     #408   +/-   ##
=======================================
  Coverage   96.22%   96.23%           
=======================================
  Files          29       29           
  Lines        3075     3105   +30     
=======================================
+ Hits         2959     2988   +29     
- Misses        116      117    +1     

Flag	Coverage Δ
Python	97.31% <97.82%> (-0.02%)	:arrow_down:
rpackage	95.65% <ø> (ø)

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Impacted Files	Coverage Δ
python/abess/bess_base.py	98.78% <96.00%> (-0.34%)	:arrow_down:
python/abess/decomposition.py	93.65% <100.00%> (ø)
python/abess/linear.py	100.00% <100.00%> (ø)
python/abess/utilities.py	100.00% <100.00%> (ø)

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