System call rework

[TheThirdOne]

This addresses #37. I made the changes to Syscall.java to implement it and then updated all of the tests and the fibonacci example to work with the new system.

I have run gradlew test and all of the tests pass with the modifications to the tests. That isn't quite conclusive that everything is working as intended though. I have not checked that each system call works as intended and there don't seem to be automated tests for that.

On my local version I also modified the error message in RISCVTests.java. The original was not helpful in finding which test I had missed.

-      assertEquals("Jupiter(0)", e.getMessage(), "failed: " + file.toString());
+      assertEquals("Jupiter(0)", e.getMessage(), "failed: " + file[0].getName());

I can also modify the documentation if you would like, but that is in a different repo so it will need to be a different PR.

[TheThirdOne]

@andrescv, is there a reason this had yet to be merged?

[MaxCrazy1101]

How to build the project? I'm new for java and riscv<3

[TheThirdOne]

@Diaosi1111, this project uses gradle to build and has a gradle wrapper set up. Just running gradlew build or gradlew.bat build will build the project.

More information about gradle can be found at https://spring.io/guides/gs/gradle/