Do not allow breaking ABI by default

[ansasaki]

Removed '--care' option and added '--allow-abi-break'. Symbols are not
removed and an Exception is raised if any symbol is removed and
'--allow-abi-break' is not used.

[codecov-io]

Codecov Report

Merging #25 into master will increase coverage by 0.57%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #25      +/-   ##
==========================================
+ Coverage   88.85%   89.42%   +0.57%     
==========================================
  Files           2        2              
  Lines         700      700              
  Branches      181      181              
==========================================
+ Hits          622      626       +4     
+ Misses         41       38       -3     
+ Partials       37       36       -1

Impacted Files	Coverage Δ
src/symbol_version/symbol_version.py	89.36% <100%> (+0.57%)	⬆️

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[coveralls]

Pull Request Test Coverage Report for Build 39

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.4%) to 91.439%

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Totals
Change from base Build 37:	0.4%
Covered Lines:	662
Relevant Lines:	700

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💛 - Coveralls

[ansasaki]

Fixes #18