refactor: QueryApi, WriteApi, WriteApiBlocking and related objects moved into api

[vlastahajek]

Refactor towards consistent API.

WriteApi,WriteApiBlocking,QueryApi interfaces and related objects like Point, FluxTableMetadata, FluxTableColumn, FluxRecord, moved to the api ( and api/write, api/query) packages.

• CHANGELOG.md updated
• Rebased/mergeable
• Tests pass

[codecov-io]

Codecov Report

Merging #125 into master will decrease coverage by 45.29%.
The diff coverage is 49.75%.

@@             Coverage Diff             @@
##           master     #125       +/-   ##
===========================================
- Coverage   86.81%   41.51%   -45.30%     
===========================================
  Files          10       20       +10     
  Lines         781     1438      +657     
===========================================
- Hits          678      597       -81     
- Misses         70      815      +745     
+ Partials       33       26        -7     

Impacted Files	Coverage Δ
api/query/table.go	43.42% <0.00%> (ø)
api/write/options.go	0.00% <0.00%> (ø)
api/write/point.go	92.94% <ø> (ø)
internal/write/writeService.go	0.00% <0.00%> (ø)
options.go	20.00% <14.81%> (-49.24%)	⬇️
compatibility.go	50.00% <50.00%> (ø)
internal/write/queue.go	85.00% <60.00%> (ø)
api/write.go	90.75% <85.00%> (ø)
api/query.go	82.67% <100.00%> (ø)
api/write/ext.go	100.00% <100.00%> (ø)
... and 17 more

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