slice: 重构 slice 中使用 equalFunc 的方法

[flycash]

1. 引入 matchFunc
2. 简化 slice 中查找类型的 API
3. 引入 Find 和 FindAll 方法

[codecov]

Codecov Report

Merging #205 (746efd1) into dev (b656686) will increase coverage by 0.26%.
Report is 1 commits behind head on dev.
The diff coverage is 96.87%.

@@            Coverage Diff             @@
##              dev     #205      +/-   ##
==========================================
+ Coverage   95.42%   95.68%   +0.26%     
==========================================
  Files          50       52       +2     
  Lines        2642     2784     +142     
==========================================
+ Hits         2521     2664     +143     
  Misses         93       93              
+ Partials       28       27       -1     

Files Changed	Coverage Δ
syncx/cond.go	95.65% <95.65%> (ø)
slice/contains.go	100.00% <100.00%> (ø)
slice/diff.go	100.00% <100.00%> (ø)
slice/find.go	100.00% <100.00%> (ø)
slice/index.go	100.00% <100.00%> (ø)
slice/map.go	100.00% <100.00%> (ø)
slice/symmetric_diff.go	100.00% <100.00%> (ø)

... and 2 files with indirect coverage changes

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