Fix of bug fixes in `rationalize.js`, also changing `simplify.js` and `simplifyConstant.js` and more 2 bugs in `simplify.js` and `simplifyconstant.js` in order to be possible passing in `Travis` test.
**Bugs in `simplifyConstant.js` and `simplify.js`**
1. `simplifyConstant.js` - I've changed `new ConstantNode(stringNumber, 'number')` to `new ConstantNode(number)`
1. `simplify.js` - Due to problems with a number node with string type, I've added `!isNaN(node.value)))` in number type test condition
**Bugs in `rationalize.js`**
3. I've fixed negative power exponents and decimals coefficients troubles. The decimals coefficients problem has led to the need to add a new feature in `simplify.js ` and `simplifyConstant.js` (next topic)
**New feature in `simplify.js` and `simplifyConstant.js`**
4. New rule type (string), whose valid values are in `listCommStrings` new variable. The only string rule accepted so far is to turn off exact fraction conversion in `simplifyConstant.js`
