* added breakpoints and stepping
* add link register to allow single-stepping a ret instruction, fix stacktraces
* refactor to avoid passing the IO layer structs to the breakpoint function
* add tests, refine the stacktrace to not include non-function
* add register information for core file parsing
* core file generation for RISC-V
* make tests run under riscv-64
* make tests run under riscv-32
