Adds support for ClouDNS (https://www.cloudns.net/)

[hbradleyiii]

Thank you for contributing to sewer.
Every contribution to sewer is important to us.
You may not know it, but you have just contributed to making the world a more safer and secure place.

Contributor offers to license certain software (a “Contribution” or multiple
“Contributions”) to sewer, and sewer agrees to accept said Contributions,
under the terms of the MIT License.
Contributor understands and agrees that sewer shall have the irrevocable and perpetual right to make
and distribute copies of any Contribution, as well as to create and distribute collective works and
derivative works of any Contribution, under the MIT License.

Now,

What(What have you changed?)

Added support for ClouDNS provider.

Why(Why did you change it?)

[codecov]

Codecov Report

Merging #122 into master will decrease coverage by 0.67%.
The diff coverage is 73.91%.

@@            Coverage Diff             @@
##           master     #122      +/-   ##
==========================================
- Coverage   86.81%   86.13%   -0.68%     
==========================================
  Files          12       13       +1     
  Lines         834      880      +46     
==========================================
+ Hits          724      758      +34     
- Misses        110      122      +12

Impacted Files	Coverage Δ
sewer/dns_providers/cloudns.py	73.91% <73.91%> (ø)