Add native String parsing methods

Hello Phil,

please merge the following String parsing methods:

```
<java.lang.Integer: int parseInt(java.lang.String)>
<java.lang.Long: long parseLong(java.lang.String)>
<java.lang.Float: float parseFloat(java.lang.String)>
<java.lang.Double: double parseDouble(java.lang.String)>
```

All test cases are passing only with one Kernel.
If I increase the amount of kernels then we have a problem.

```java
for(int i = 0; i < 5; ++i) {
  ret.add(new StringToDoubleRunOnGpu(Double.toString(Math.pow(0.125, i))));
}

[TEST 1/1] org.trifort.rootbeer.testcases.rootbeertest.serialization.StringToDoubleTest@3fcd44f3
  0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 
 16: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 
 32: ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 
 48: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
 64: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
 80: 01 00 00 00 00 0f 00 00 30 00 00 00 00 00 00 00 
 96: ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 00 
112: 08 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
128: 00 00 00 00 4a 0b 00 00 20 00 00 00 00 00 00 00 
144: ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 00 
160: 0a 00 00 00 24 10 00 00 2c 00 00 00 03 00 00 00 
176: ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 00 
192: 31 00 00 00 2e 00 00 00 30 00 00 00 00 00 00 00 
208: 01 00 00 00 00 0f 00 00 30 00 00 00 00 00 00 00 
224: ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 00 
240: 10 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
java.lang.NullPointerException
	at org.trifort.rootbeer.runtime.CUDAContext.readBlocks(CUDAContext.java:254)
	at org.trifort.rootbeer.runtime.CUDAContext.run(CUDAContext.java:180)
	at org.trifort.rootbeer.runtime.Rootbeer.run(Rootbeer.java:105)
	at org.trifort.rootbeer.test.RootbeerTestAgent.test(RootbeerTestAgent.java:195)
	at org.trifort.rootbeer.test.RootbeerTestAgent.testOne(RootbeerTestAgent.java:44)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:597)
	at org.trifort.rootbeer.entry.RootbeerTest.runTests(RootbeerTest.java:55)
	at org.trifort.rootbeer.entry.Main.run(Main.java:170)
	at org.trifort.rootbeer.entry.Main.main(Main.java:211)
  FAILED
  Exception thrown at index: 0
```
I thought you solved this multiple kernel issue already?

Thanks!

Martin