Add unset on navigators

[nlepage]

Description

Add unset operation on navigators, and use it in unset.

Issue : fix #305

[frinyvonnick]

This is barely the same code as in the indexNav. Can we do something about it ?

[nlepage]

Yes this is exactly the same code as in IndexNav, and we could mutualize it in their common ancestor BaseNav.
But for comprehension sake, I think it is better to have two copies of this method, one that uses an index which denotes an array access, and one that uses a key which denotes a property access.

[codecov-io]

Codecov Report

Merging #318 into dev will decrease coverage by 0.49%.
The diff coverage is 90.9%.

@@            Coverage Diff            @@
##              dev     #318     +/-   ##
=========================================
- Coverage   97.17%   96.68%   -0.5%     
=========================================
  Files         107      108      +1     
  Lines         425      452     +27     
=========================================
+ Hits          413      437     +24     
- Misses         12       15      +3

Impacted Files	Coverage Δ
packages/immutadot/src/nav/nav.js	87.5% <ø> (-4.17%)	⬇️
packages/immutadot/src/nav/propNav.js	100% <100%> (ø)	⬆️
packages/immutadot/src/core/unset.js	100% <100%> (ø)	⬆️
packages/immutadot/src/nav/baseNav.js	100% <100%> (ø)	⬆️
packages/immutadot/src/nav/finalNav.js	100% <100%> (ø)
packages/immutadot/src/nav/indexNav.js	94.44% <80%> (-5.56%)	⬇️
packages/immutadot/src/nav/propsNav.js	85% <87.5%> (+1.66%)	⬆️
packages/immutadot/src/nav/sliceNav.js	96.15% <87.5%> (-3.85%)	⬇️

---

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 27b9903...bbcb9ea. Read the comment docs.