✨ Add FlipSign bridges

[blegat]

Closes #516

[codecov-io]

Codecov Report

Merging #658 into master will increase coverage by 0.12%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #658      +/-   ##
==========================================
+ Coverage   94.84%   94.96%   +0.12%     
==========================================
  Files          49       50       +1     
  Lines        5296     5345      +49     
==========================================
+ Hits         5023     5076      +53     
+ Misses        273      269       -4

Impacted Files	Coverage Δ
src/Bridges/flip_sign_bridge.jl	100% <100%> (ø)
src/Bridges/Bridges.jl	100% <100%> (ø)	⬆️
src/Utilities/functions.jl	96.59% <100%> (+0.05%)	⬆️
src/Bridges/slackbridge.jl	100% <0%> (ø)	⬆️
src/Bridges/quadtosocbridge.jl	93.93% <0%> (+3.03%)	⬆️
src/Bridges/vectorizebridge.jl	97.22% <0%> (+5.55%)	⬆️

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