Feature/client ipnat

[jcbf]

ClientIPNAT allows IP address translation of the connecting IP
This is particularly useful when you have internal email flows and still have an SPF evaluation

[codecov]

Codecov Report

Merging #74 into master will decrease coverage by 1.28%.
The diff coverage is 86.48%.

@@            Coverage Diff             @@
##           master      #74      +/-   ##
==========================================
- Coverage   90.72%   89.43%   -1.29%     
==========================================
  Files           1        1              
  Lines         550      587      +37     
==========================================
+ Hits          499      525      +26     
- Misses         51       62      +11     

Impacted Files	Coverage Δ
smf-spf.c	89.43% <86.48%> (-1.29%)	⬇️

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[coveralls]

Coverage decreased (-1.3%) to 89.562% when pulling adcdcda on feature/ClientIPNAT into 6419984 on master.