Implemented class JitPlatform

Implemented class JitPlatform. It improves abstraction level
from Jit library. If I want to change Jit library I have
to change all references to old jit library to references
to new jit library. That was earlier. Now all references
to jit library's functions replaced with references to
functions of JitPlatform class. Functions of JitPlatform
class calls corresponding functions of jit library.
It means that if I want to change jit library I just
have to change some single references in JitPlatform
class functions.