Adding user space memory allocation functions and refactoring syscalls

- sbrk & brk added
- Renamed some syscall datasets
- Added malloc function

Signed-off-by: Olli Vanhoja <olli.vanhoja@gmail.com>
Adding string lib for user space and some refactoring

- Moving files around to make dir structure better
- Renamed markdown files
- Added string directory cotaining platform independent string functions
- Minor changes in header files
Renamed src to kern