Improved multiline string handling

[Arakos]

The multiline yaml-value change detection is currently not very useful (especially if color mode is off/not available) for huge text blocks (i.e. scripts, config-files, etc.) that are stored in a multiline string value.

Multiline string values will now render added/removed/changed lines as the string change detection logic go-diff detects. Unchanged lines will be truncated. Amount of unchanged lines to render around changes can be configured, default is 4.

Changes:

• refactor the multiline string diff handling
• tackle issue-123 in go-diff lib by updating to current, as of yet untagged master build containing the fix in pull-request 136
• adapt existing testcases accordingly
• add additional, more complex multiline testcase

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (292c5cf) 82.79% compared to head (d4d9ed1) 82.86%.
Report is 10 commits behind head on main.

Files	Patch %	Lines
pkg/dyff/output_human.go	96.22%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #333      +/-   ##
==========================================
+ Coverage   82.79%   82.86%   +0.06%     
==========================================
  Files          14       14              
  Lines        1843     1862      +19     
==========================================
+ Hits         1526     1543      +17     
- Misses        254      255       +1     
- Partials       63       64       +1     

Flag	Coverage Δ
unittests	82.86% <96.66%> (+0.06%)	⬆️

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[gotwarlost]

This is such a lovely addition to an already awesome tool. Any chance of getting this merged?