feat: allow to obtain the stack trace as a string

[sergiud]

Expose DumpStackTraceToString as GetStackTrace.

Resolves #144

[codecov-commenter]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (68b6ce3) 59.60% compared to head (755bec4) 59.57%.
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1075      +/-   ##
==========================================
- Coverage   59.60%   59.57%   -0.03%     
==========================================
  Files          19       19              
  Lines        2604     2605       +1     
  Branches      914      915       +1     
==========================================
  Hits         1552     1552              
- Misses        712      713       +1     
  Partials      340      340              

Files	Coverage Δ
src/glog/logging.h	64.28% <ø> (ø)
src/logging.cc	66.81% <100.00%> (-0.03%)	⬇️
src/utilities.h	100.00% <ø> (ø)
src/utilities.cc	71.55% <80.00%> (-0.41%)	⬇️