refactor: Renaming InfluxDBClient -> Client

[vlastahajek]

Renamed InfluxDBClient interface to Client, so the full name influxdb2.Client suits better to Go naming conventions

Closes #103

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

[codecov-io]

Codecov Report

Merging #107 into master will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #107      +/-   ##
==========================================
+ Coverage   86.77%   86.81%   +0.03%     
==========================================
  Files          11       11              
  Lines         779      781       +2     
==========================================
+ Hits          676      678       +2     
  Misses         70       70              
  Partials       33       33              

Impacted Files	Coverage Δ
client.go	93.10% <100.00%> (ø)
query.go	87.56% <100.00%> (ø)
setup.go	73.68% <100.00%> (+1.46%)	⬆️
write.go	94.06% <100.00%> (ø)
writeApiBlocking.go	82.60% <100.00%> (ø)
writeService.go	77.67% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 5563857...5622f46. Read the comment docs.