ENH: Add from_arrays for MultiIndex

[charlesdong1991]

I was trying to create a MultiIndex from an array just now, and found out it hadnt been implemented, so have this PR to create MI from arrays.

>>> arrays = [['a', 'a', 'b', 'b'], ['red', 'blue', 'red', 'blue']]
>>> ks.MultiIndex.from_arrays(arrays)
MultiIndex([('a',  'red'),
                    ('a', 'blue'),
                    ('b',  'red'),
                    ('b', 'blue')],
                   names=['number', 'color'])

[itholic]

ks..MultiIndex.from_arrays(arrays, names=('number', 'color'))

2144

2145 ^

2146

2147SyntaxError: invalid syntax

2148

2149/home/travis/build/databricks/koalas/databricks/koalas/indexes.py:595: 

Maybe here is the problem ?

ks.. -> ks. 😄

[charlesdong1991]

hahaha, yeah, my bad. I didn't check carefully and then went to bed because i was too sleepy yesterday. @itholic

[itholic]

haha. yeah that is also happening to me often. 😄

[codecov-io]

Codecov Report

Merging #1001 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1001      +/-   ##
==========================================
+ Coverage   94.79%   94.79%   +<.01%     
==========================================
  Files          34       34              
  Lines        6572     6575       +3     
==========================================
+ Hits         6230     6233       +3     
  Misses        342      342

Impacted Files	Coverage Δ
databricks/koalas/indexes.py	96.41% <100%> (+0.05%)	⬆️

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[ueshin]

@charlesdong1991 Shall we keep the example in the first commit with doctest: +SKIP?
Otherwise, LGTM.

[charlesdong1991]

oh, okay 😅

[ueshin]

oh, sorry, please fix ks.Multi. 😄
also nit: style. need 2 spaces before #.

[charlesdong1991]

oh, god, sorry 😅

[ueshin]

LGTM, pending tests.

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[ueshin]

Thanks! merging.