Some code style fixes and validating positive number regexp fix

Author: Vaidas Lažauskas

src/BcMath.php

@@ -68,7 +68,7 @@ public function getScale()
      * @param BcMath_Number|string $leftOperand
      * @param BcMath_Number|string $rightOperand
      *
-     * @return BcMath_Number The sum of the two operands, as a string.
+     * @return string The sum of the two operands, as a string.
      */
     public function addition($leftOperand, $rightOperand)
     {
@@ -87,7 +87,7 @@ public function addition($leftOperand, $rightOperand)
      * @param BcMath_Number|string $leftOperand
      * @param BcMath_Number|string $rightOperand
      *
-     * @return BcMath_Number The result of the subtraction, as a string.
+     * @return string The result of the subtraction, as a string.
      */
     public function subtraction($leftOperand, $rightOperand)
     {

src/BcMath/Command/Addition.php

@@ -30,5 +30,4 @@ public static function process(BcMath_Number $left, BcMath_Number $right, BcMath
             $command($left->getValue(), $right->getValue(), $scale->getValue())
         );
     }
-
 }

src/BcMath/Command/Comparison.php

@@ -30,5 +30,4 @@ public static function process(BcMath_Number $left, BcMath_Number $right, BcMath
             $command($left->getValue(), $right->getValue(), $scale->getValue())
         );
     }
-
 }

src/BcMath/PositiveNumber.php

@@ -16,7 +16,7 @@ class BcMath_PositiveNumber extends BcMath_Number
      */
     public function isValid($number)
     {
-        return (boolean) preg_match('/^\d+$/', $number);
+        return (boolean) preg_match('/^\d+(\.\d+)?$/', $number);
     }
 
     /**