Committed fixes for stack_walker according to dwarf data parser changes (also : build fixing)

Function address should be used as a key of dwarf data

Removed forgotten debug

Store function base address as a function_data_t id

Added unittest for dwarf data obraining during unwind

Try to collect dwarf data during the unwind process

Separate function_data_t into the dedicated module

Rfg StackWalker. Now it inherits vector, instead of including it

Added an extra test for stack_walker

Replaced vector (for storing dwarf function data) by unordered_set

Do not add nullptr stack segment to the unwind result, since it means an end-of-the-stack in libunwind therms; also small rfg

Rfg of stack_walker (and the stack_walker's unittest)

Added test_recursion test; made a small rfg

Added ybtl stack walker

Small code cleanup