Handle float type in positive number (CLIUtils#328)

[ChristosT]

This PR enables checking positivity of float types , providing a fix to #328.
Numbers are handled as doubles in the same way that CLI:Number is structured

CLI11/include/CLI/Validators.hpp

Lines 364 to 369 in 418b717

	class Number : public Validator {
	public:
	Number() : Validator("NUMBER") {
	func_ = [](std::string &number_str) {
	double number;
	if(!detail::lexical_cast(number_str, number)) {

Also, aCLI:NonNegative is added and checks if number <=0 while CLI:Positive is modified to check whether number>0

[codecov]

Codecov Report

Merging #342 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #342   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          12     12           
  Lines        3331   3341   +10     
=====================================
+ Hits         3331   3341   +10

Impacted Files	Coverage Δ
include/CLI/Validators.hpp	100% <100%> (ø)	⬆️

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[henryiii]

Thanks!