Fixed get() and opt() inconsistency

[nayak-yash]

What does this PR do ?

This PR fixes the optLong() - getLong() and optDouble() and getDouble() inconsistencies
Fixes #653

Type of change

Previously stringToNumber() checked for strings starting with either digit or - . Now it only checks for whether the string is a decimal number or integer.

Passed all test cases

Other information

JSONObject object1 = new JSONObject("{\"number\":\"-.1234\"}");
JSONObject object2 = new JSONObject("{\"number\":\"-0000000.32879\"}");
JSONObject object3 = new JSONObject("{\"number\":\"-07.89\"}");
JSONObject object4 = new JSONObject("{\"number\":\"-0.00000000\"}");
System.out.println("1. getDouble() = " + object1.getDouble("number"));
System.out.println("1. optDouble() = " + object1.optDouble("number"));
System.out.println("2. getDouble() = " + object2.getDouble("number"));
System.out.println("2. optDouble() = " + object2.optDouble("number"));
System.out.println("3. getDouble() = " + object3.getDouble("number"));
System.out.println("3. optDouble() = " + object3.optDouble("number"));
System.out.println("4. getDouble() = " + object4.getDouble("number"));
System.out.println("4. optDouble() = " + object4.optDouble("number"));

Output :

1. getDouble() = -0.1234
1. optDouble() = -0.1234
2. getDouble() = -0.32879
2. optDouble() = -0.32879
3. getDouble() = -7.89
3. optDouble() = -7.89
4. getDouble() = -0.0
4. optDouble() = -0.0

[stleary]

@nayak-yash Thanks for submitting this PR, but #783 has already been accepted to fix this bug. Your fix also successfully addressed the bug, however, the other solution was preferred because the code changes were directly related to the bug fix, and numerous unit tests were added. Please feel free to pick another issue and work on that.