Turn "123,456 %" into just "123.456"!

Mainly for use in C# to parse percentage as string into double.

• Strip away whitespace
• Replace comma with decimal point
• Only allow valid numeric input
  • multiple commas or decimal points won't match
    • therefore does not support thousands-grouping, not even spaces, sorry
  • multiple % symbols won't match
  • any character not 0-9, ,, . or % won't match
  • + or - will match, but +- or ± will not, nor will any other operators
• Using $1$2.$3$4 for substitution spits out a sanitized number with a forced decimal point.

Note: The decimal point is present even when the number input doesn't include any decimals, e.g. for 12% the result will be 12.. You may wish to append a 0 in your code to make it 12.0 - in .NET 4.5 C# the double.Parse and double.TryParse handle the result just fine even without that, but your mileage may vary.

See example on repl.it