Implement Series.drop

[itholic]

Resolves #822

Like pandas Series.drop (https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.Series.drop.html#pandas.Series.drop)

I implemented drop function for series.

Example:

>>> s = ks.Series(data=np.arange(3), index=['A', 'B', 'C'])
>>> s
A    0
B    1
C    2
Name: 0, dtype: int64
>>>
>>> s.drop('A')
B    1
C    2
Name: 0, dtype: int64
>>>
>>> s.drop(labels=['B', 'C'])
A    0
Name: 0, dtype: int64

Also Support for MultiIndex

>>> midx = pd.MultiIndex(levels=[['lama', 'cow', 'falcon'],
...                              ['speed', 'weight', 'length']],
...                      codes=[[0, 0, 0, 1, 1, 1, 2, 2, 2],
...                             [0, 1, 2, 0, 1, 2, 0, 1, 2]])
>>> s = ks.Series([45, 200, 1.2, 30, 250, 1.5, 320, 1, 0.3],
...               index=midx)
>>> s
lama    speed      45.0
        weight    200.0
        length      1.2
cow     speed      30.0
        weight    250.0
        length      1.5
falcon  speed     320.0
        weight      1.0
        length      0.3
Name: 0, dtype: float64

>>> s.drop(labels='weight', level=1)
lama    speed      45.0
        length      1.2
cow     speed      30.0
        length      1.5
falcon  speed     320.0
        length      0.3
Name: 0, dtype: float64

(above examples are using pandas one)

[codecov-io]

Codecov Report

Merging #829 into master will increase coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master    #829      +/-   ##
=========================================
+ Coverage   94.27%   94.3%   +0.02%     
=========================================
  Files          34      34              
  Lines        6150    6181      +31     
=========================================
+ Hits         5798    5829      +31     
  Misses        352     352

Impacted Files	Coverage Δ
databricks/koalas/missing/series.py	100% <ø> (ø)	⬆️
databricks/koalas/series.py	95.33% <100%> (+0.25%)	⬆️

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[itholic]

@ueshin I just resolved build failure here related with python 3.5 compatibility. Could you check this PR if maybe when you available? 😄

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[ueshin]

LGTM.

[ueshin]

Thanks! merging.

[itholic]

@ueshin Thanks for reviewing this 😃