Puncover will now unmangle cpp symbol names

[sarfata]

This requires an external tool (c++filt) which is called every time the elf is reparsed with the list of all the symbols.

It is enabled all the time because it knows to not change C symbols.

This PR closes #3.

Before:

After:

[codecov-io]

Codecov Report

Merging #4 into master will decrease coverage by 1.19%. The diff coverage is 11.11%.

@@            Coverage Diff            @@
##           master       #4     +/-   ##
=========================================
- Coverage   69.07%   67.87%   -1.2%     
=========================================
  Files          12       12             
  Lines        1051     1074     +23     
=========================================
+ Hits          726      729      +3     
- Misses        325      345     +20

Impacted Files	Coverage Δ
puncover/puncover.py	0% <0%> (ø)	:arrow_up:
puncover/collector.py	70% <15.78%> (-1.05%)	:arrow_down:
puncover/renderers.py	35.19% <7.14%> (-1.71%)	:arrow_down:

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[HBehrens]

Regarding my comment about lazy-initialization: I didn't realize that you are calling c++filt only once with the entire list. Maybe that's not so much of a bottleneck and initializing this lazily is not worth it all.

[sarfata]

I think I have addressed all your comments. Let me know what you think.