Adding optional barriers to tic!

[amartinhuertas]

@fverdugo ... ready to merge

[codecov-commenter]

Codecov Report

Merging #47 (a4fd14d) into master (2a06ba4) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #47      +/-   ##
==========================================
+ Coverage   91.69%   91.72%   +0.02%     
==========================================
  Files           7        7              
  Lines        2084     2091       +7     
==========================================
+ Hits         1911     1918       +7     
  Misses        173      173              

Impacted Files	Coverage Δ
src/PTimers.jl	96.38% <100.00%> (+0.33%)	⬆️

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[amartinhuertas]

@fverdugo ... this PR is still pending ... please proceed whenever you have time ... thanks!