Add poll API

[moko256]

Detail docs for API is this:

• get/vote poll
• post poll
• poll entity
• poll in the status

[codecov-io]

Codecov Report

Merging #84 into master will decrease coverage by 2.05%. The diff coverage is 0%.

@@             Coverage Diff              @@
##             master      #84      +/-   ##
============================================
- Coverage      49.6%   47.54%   -2.06%     
  Complexity      148      148              
============================================
  Files            47       49       +2     
  Lines           877      915      +38     
  Branches         95       98       +3     
============================================
  Hits            435      435              
- Misses          425      462      +37     
- Partials         17       18       +1

Impacted Files	Coverage Δ	Complexity Δ
...ava/com/sys1yagi/mastodon4j/api/method/Statuses.kt	69.56% <0%> (-14.65%)	11 <0> (ø)
...n/java/com/sys1yagi/mastodon4j/api/method/Polls.kt	0% <0%> (ø)	0 <0> (?)
.../java/com/sys1yagi/mastodon4j/api/entity/Status.kt	35.48% <0%> (-1.19%)	6 <0> (ø)
...in/java/com/sys1yagi/mastodon4j/api/entity/Poll.kt	0% <0%> (ø)	0 <0> (?)

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