GJKResult/API changes

[tkoolen]

Remove the signed_distance field from GJKResult, add in_collision and weights fields. Main reasons:

• penetration distance computation often accounts for a a significant fraction of total computation time, while there are cases where it's not even needed. So make computing it optional by having it be in a separate method
• I find the term signed_distance to be a bit disingenuous; in penetration we're not actually computing proper penetration distance. By having separate separation_distance and simplex_penetration_distance functions and talking about the difference in the readme, we're no longer lying.

[codecov-io]

Codecov Report

Merging #27 into master will decrease coverage by 1.87%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master      #27      +/-   ##
==========================================
- Coverage   94.54%   92.67%   -1.88%     
==========================================
  Files           8        8              
  Lines         220      232      +12     
==========================================
+ Hits          208      215       +7     
- Misses         12       17       +5

Impacted Files	Coverage Δ
src/EnhancedGJK.jl	100% <ø> (ø)	⬆️
src/gjk.jl	93.18% <66.66%> (-5.51%)	⬇️

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