Improve Validation callbacks/usage

[adhocore]

• callbacks bound to main instance
• validator options can be accessed $this->getOption(...)
• currently validated value can be accessed directly $this->getCurrentValue()

[codecov-io]

Codecov Report

Merging #10 into master will not change coverage. The diff coverage is 0%.

@@          Coverage Diff           @@
##             master   #10   +/-   ##
======================================
  Coverage         0%    0%           
- Complexity      239   244    +5     
======================================
  Files            19    19           
  Lines           579   591   +12     
======================================
- Misses          579   591   +12

Impacted Files	Coverage Δ	Complexity Δ
src/Validation/Validation.php	0% <0%> (ø)	32 <7> (+5)	:arrow_up:

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