ENH: Support non TLS connection

[Miksus]

This PR includes enhancements to make the server configuration more customizable.

See: this issue

[Miksus]

Probably could help to have a couple of words in docs.

[codecov-commenter]

Codecov Report

Merging #11 (dec884a) into master (614ef18) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master      #11   +/-   ##
=======================================
  Coverage   99.18%   99.19%           
=======================================
  Files          12       12           
  Lines         491      496    +5     
=======================================
+ Hits          487      492    +5     
  Misses          4        4           

Impacted Files	Coverage Δ
redmail/email/sender.py	99.29% <100.00%> (+0.02%)	⬆️

---

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 614ef18...dec884a. Read the comment docs.