Add AbstractOptimizationResult

[goerz]

This allows for more seamless conversion between the result objects of different methods. To convert between two result types, the first result is converted to a Dict of field names to values, and then that dict is converted to the target result type. This assumes that all result types have a common set of field names, and for any field in a result that is not in that common set, a custom convert method must be defined that sets default values for those fields in the target result type.

[codecov]

Codecov Report

Attention: Patch coverage is 94.44444% with 2 lines in your changes missing coverage. Please review.

Project coverage is 88.6%. Comparing base (71b6197) to head (b18e3e2).

Files with missing lines	Patch %	Lines
src/result.jl	93.2%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           master     #78     +/-   ##
========================================
+ Coverage    88.5%   88.6%   +0.2%     
========================================
  Files          19      20      +1     
  Lines        1001    1030     +29     
========================================
+ Hits          885     912     +27     
- Misses        116     118      +2     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.