Drop PHP 7.0 and 5.x support

[AydinHassan]

• Minimum PHP version now 7.1
• Updated dependencies
• Remove useless @package + Class doc blocks
• Add type hints everywhere and removed useless assertions + remove doc block hints
• Added phpstan to build

[codecov-io]

Codecov Report

Merging #79 into master will increase coverage by 0.55%.
The diff coverage is 89.47%.

@@             Coverage Diff              @@
##             master      #79      +/-   ##
============================================
+ Coverage     88.57%   89.13%   +0.55%     
- Complexity      241      246       +5     
============================================
  Files            18       18              
  Lines           735      690      -45     
============================================
- Hits            651      615      -36     
+ Misses           84       75       -9

Impacted Files	Coverage Δ	Complexity Δ
src/Action/ExitAction.php	100% <100%> (ø)	1 <1> (ø)	⬇️
src/MenuItem/SelectableItem.php	100% <100%> (ø)	4 <4> (+1)	⬆️
src/MenuItem/LineBreakItem.php	100% <100%> (ø)	9 <9> (+1)	⬆️
src/Dialogue/Confirm.php	100% <100%> (ø)	2 <2> (ø)	⬇️
src/MenuItem/MenuMenuItem.php	100% <100%> (ø)	5 <5> (+1)	⬆️
src/Util/StringUtil.php	100% <100%> (ø)	5 <5> (ø)	⬇️
src/Dialogue/Flash.php	100% <100%> (ø)	1 <1> (ø)	⬇️
src/Action/GoBackAction.php	100% <100%> (ø)	2 <2> (ø)	⬇️
src/CliMenuBuilder.php	98.55% <100%> (-0.16%)	43 <39> (-2)
src/MenuItem/AsciiArtItem.php	100% <100%> (ø)	13 <9> (+1)	⬆️
... and 15 more

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[mikeymike]